Even though WWE will not use this explanation, given its adoration of the Three Month Rule, there is a logical reason for Seth Rollins breaking up The Shield. Remember, the group's original purpose was the keep the WWE Universe from getting what it wanted. If Seth Rollins is indeed the architect of The Shield, it would make sense for him to break away from it when the fans got firmly behind the group.
The Authority wanting Randy Orton to win the World Heavyweight Championship ladder match and Seth Rollins to win the traditional Money in the Bank match. At first, you might wonder why The Authority would seemingly be setting their favorites against each other—since Rollins would have to cash in on Orton and thus cause tension and dissension between them—before you realize that they likely weren't going to let Rollins cash in at all had Orton won; they wanted Orton to win the title and Rollins to win the contract to keep it out of the hands of the rest of the wrestlers to protect Orton from having an "undesirable" cash-in on him and possibly take the title off him. Since Orton lost, however, Rollins has turned into the ace up their sleeves—while they continue to try to set things up for Orton to win, they can still position Rollins to win the title as a back-up plan when the moment is right, and if Orton continues to disappoint, they can simply shift all their favor to Rollins. This appeared to be coming to fruition before the new year, as Rollins once came close to cashing in for the title on BROCK LESNAR and Orton was deployed to protect Rollins, much to The Viper's dismay. Rollins eventually outright replaced Orton as The Authority's top guy and became the spark of life Cena's and Lesnar's rivalry needed as the third man in their title match at Royal Rumble 2015, then…well, see what happened below with Plan B.
In listening to the Journey to Summerslam: Destruction of the Shield special and some of the recounts of Seth's FCW/NXT career, where Triple H and others reference Rollins as a guy whose anxiousness to prove himself as the best brought him into conflict with people around him, a lot of Rollins's on-screen actions start to seem less and less out-of-character.
Coming out of Royal Rumble 2015, it was painfully obvious that WWE wanted Reigns to go over Lesnar and win the title. But after the fans reacted badly to what they felt was a forced push, the WWE probably realized that having Reigns beat Lesnar clean would kill any chance Reigns had of ever becoming a top face. And thus the cash-in plan was hatched. Get the title off Brock without Lesnar being pinned by having Rollins cash-in during the match after both competitors were spent, making it a Triple Threat, and have Rollins pin Reigns for the win. This seemed to be a late audible, but perhaps one that they had in their pocket for a situation like this - or, in other words, Plan B.
This happened again in 2016, not long after Seth returned from his knee injury. The combination of Finn Bálor blowing out a shoulder in the process of winning the new WWE Universal Championship against Rollins with Reigns being suspended/in WWE's doghouse for a Wellness Violation meant they needed a new main-event face. So they decided to turn Rollins and pit him against new champ Kevin Owens a couple of weeks later, when it had been obvious to that point that Rollins was meant to remain heel. Similarly to how he, as a member of The Shield, took out Evolution and replaced them at Triple H's side a few weeks later, he also "took out" Finn Balor as the new top babyface on RAW and ended up having to take his spot.
During the two matches between Evolution (Randy Orton, Batista, and Triple H) and The Shield (Roman Reigns, Seth Rollins, and Dean Ambrose), Triple H and Rollins spent a lot of time fighting another. Besides the somewhat more obvious theme of "Mastermind of The Shield vs. Mastermind of Evolution," this may have been the reason Triple H chose Seth Rollins to not only orchestrate The Shield's destruction but also to be the face of WWE.
Seth Rollins's character shows an interesting dichotomy between a cold, calculated schemer and a petulant, impulsive Manchild. He's probably earned himself as many natural enemies as can be earned by a single individual in a wrestling storyline. And yet, with all of those enemies, he's always been able to survive. Why? Because those enemies also have to interact with each other, and with so many people involved as well as his championship title, the personal conflicts combined with the natural professional rivalries that would occur from two or more people wanting to chase the championship shot, all ensure that his enemies all have to deal with each other before they come after him.
Seth being a petulant Manchild also explains why it took so long to start between when he first went down with injury and when he finally became a true babyface.
"Redesign, Rebuild, Reclaim" was the new philosophy he took to his recovery and return. "Reclaim" being the endgame signifies that the entire focus was fixing what cost him the WWE World Heavyweight Championship and then obtaining said championship back. What cost him the title? His own lapse of judgement in trying a second-rope sunset flip powerbomb to a resistant Kane and his knee collapsing as a result. "Redesign" meant get smarter and "Rebuild" meant get that knee back to 100%. Triple H moving to adapt and replace him with a new champion near instantly after he went down didn't affect him at all because the Authority had nothing to do with his losing the gold; on the contrary, they had his back when he was active and champion, and if they could replace him that quickly when he went out, they would embrace him again that much faster when he came back, as he envisioned it, even better than before.
When Rollins returned to action, he trolled and rejected the fans despite the fact that his much-anticipated return and going against Roman Reigns made him the most popular wrestler in the company overnight. Why? Because he knew he could still ingratiate himself to Stephanie McMahon due to her Vince-inherited addiction to enforcing a certain vision through power and control. Steph initially "keeping things professional" was all to placate her brother Shanenote who Vince installed as her rival commissioner on SmackDown and Mick Foleynote who she hired to be the likable General Manager and make her look good; and as soon as he demonstrated he was good enough to only need subtle help from her, she'd be back on his side. True to form, he defeated Roman Reigns semi-cleanly on his own to reclaim his title, at least for two minutes, anyway, thanks to Dean Ambrose and a golden briefcase. However, that didn't help him out much when it came to Triple H…
Between getting cashed in on by Ambrose exactly the way Dean said he would; failing to get back the championship from Ambrose before the draft took hold and thus losing it to SmackDown, which forced Raw to create a brand new top title from scratch; and injuring top NXT draft pick Finn Bálor in the first Universal Championship title match while failing to win and pick up said championship; there's plenty of reason things would be on the rocks between Rollins and either Helmsley. However, Stephanie seemed to put most of the blame on Roman Reigns, whereas Triple H never appeared to speak on the matter until he took Roman out with a Pedigree to help Rollins eliminate him in a four-way match for the vacant championship…only to betray Rollins with another Pedigree to give Kevin Owens the victory.
Rollins stated in later weeks that he knew Hunter would do something like this despite his confident grin after Triple H helped him take out Reigns and his persisting implacable anger after Hunter betrayed him. However…he also said that he expected better from Stephanie. Given that she's both Triple H's marital and professional partner, that totally makes sense: Hunter would've told her what he was planning to do with the man they'd invested several years in molding to the top, and she would've at least tipped Seth off subtly that Hunter was angry at him. At the very least, he'd have to ease Steph's concerns by pretending he still liked Seth for more than two minutes before dropping the bomb. Right? Well…they're still the McMahon-Helmsley duo and he just made the lethally stupid mistake of underestimating their duplicity — or overestimating his own importance to them. Rollins wasn't merely upset at them for betraying him or costing him the championship but rather for humiliating him.
The above point also explains why Rollins kept on acting like a heel despite playing the role of a face when he first wanted revenge for the betrayal. If the act in and of itself wasn't what surprised him or set him off, of course it wouldn't have actually taught him anything. He was still the same entitled prat they used to call "the Undisputed Future of WWE", only his childish fury was now pointed against the circle of power — and between Stephanie, Owens, and Chris Jericho, and the fact that Hunter went right back to the shadows of NXT after dropping him, he had plenty of reason to stay hot-headed. Being re-injured at the hands of Triple H's new hitman Samoa Joe, however, finally forced Rollins to take a step back from the trees to see the forest in front of him. That's when the Heel Realization of who he'd become finally, at long last, truly hit him—prompting an actual change back into a variant of his previous honorable persona, now taking on the cause of a Kingslayer seeking redemption.
Pulling all this back full circle, his WrestleMania 33 outfit consisted of a golden version of his standard post-Shield gear…with a few disheveled gray designs with black outlines almost looking like it was deliberately burned/torn open into these shapes. Said shapes including a shield with his stylized SR logo on it burned right into the chest and stomach of the outfit. If, as he said, he's trying to recover who he was before Triple H corrupted him…this deliberate homage confirms that yes, The Shield did mean something to him.
The King's Landing knee makes more sense as a finisher remembering that Seth legitimately destroyed Cena's nose with a knee once.
If you look closely at the 'Beastslayer' logo that comes up on Seth's Titantron animation, you'll notice that Seth's 'sigil' is inlaid with a pair of crossed swords. He earned the sobriquet by fighting (figuratively "crossing swords") and beating "The Beast", who is known for having a prominent sword tattoo on his chest...
Wrestlemania 40, Night 2’s Main Event, full stop. Seth came out to the Shield’s theme music and dressed in the tactical vest and ring gear of the group to help Cody and he took a chair shot to the back from Reigns that called back to his betrayal of The Shield down to the selling of the hit. And what did Roman Reigns say he could never forgive Rollins for? And it cost Reigns the match. Seems like Rollins managed to weaponize Roman’s Berserk Button. Seth himself told Cody, he was willing to be "His Shield", and he did just that.
On reflection of it, it seems less that Seth was expecting to be able to rescue Cody, having gone through hell twice and being absolutely spent, more that his plan was to give Cody one final opening by hitting the nerve Roman will never get over, by getting both himself and a chair into the ring.
