There were many reasons why American Idol flew off the rails in the later seasons... and looking back, most of them were there almost from the start.
- This article from Maura Johnston of The Concourse, analyzing the show's decline over the course of its run, points to a number of events in the earlier, popular seasons that foreshadowed how, in later seasons, the show and its voters would increasingly fall out of step with the pop music mainstream. The Shocking Elimination of Jennifer Hudson very early in season 3 — and her going on to have the biggest career out of anyone that season — is regarded as the first crack, especially given the allegations that her elimination was due to racial bias (Hudson being a black R&B singer), but the true tipping point was the victory of Taylor Hicks in season 5. Hicks, a soul singer whose style couldn't have been more different from contemporary pop music trends, won largely due to the show's older voters who rejected said modern pop, and sure enough, he ended up swiftly fading from popular culture after his one post-Idol hit. From then on, singers with modern pop or R&B sensibilities found it harder to stay in the game as the show's graying core voter base favored "white guys with guitars", i.e. young, attractive, non-threatening white guys (often from the Bible Beltnote ) with soft vocals who performed acoustic ballads in the vein of Jason Mraz or John Mayer. Such artists usually left no presence on the pop charts; season 10 winner Scotty McCreary having success in Country Music but no pop crossover hits, and season 11 winner Phillip Phillips becoming a Two-Hit Wonder with "Home" and "Gone Gone Gone", was about the best they ever realistically hoped for. The jump-the-shark moment in season 8, when Kris Allen won a Dark Horse Victory over Adam Lambert (and under fairly suspicious circumstances, at that), was merely the moment at which this became readily apparent even to the show's fans. The pop music world abandoned the show, sponsors followed suit, and ratings (especially in the key 18-49 demographic) plunged, leading to a growing number of gimmicks and stunt-cast judges in an attempt to keep the show relevant against competitors like The Voice. Eventually, it was announced that season 15 in 2016 would be the last, at least before its revival on ABC in 2018.
- Another factor that bedeviled Idol during its run, one that was closely linked to the above, was the fact that its boom years coincided with the rise of the internet, which the show's creators never really figured out how to properly interact with. In the first couple of seasons, when most households only had dial-up (if anything) and Web 2.0 was still barely a blip on the radar, this wasn't an issue. However, Idol continued to ignore the internet at its peril, which caused two critical problems. First, it isolated the show from a new generation of young people, who engaged with social media at a far greater rate than their predecessors. Without a serious online presence even in the '10s, the show may as well have not existed to them except as something that their parents watched. As a result, the average viewer age slowly crept up from 31 in the first season to 44 in the eighth to 51 in the twelth (i.e. outside the 18-49 demographic), and the show's most successful finalists increasingly began to reflect the tastes of the show's older voters even though they saw little pop stardom afterwards. Second, it allowed snark blogs to become the face of the show's "fandom" online. The most infamous such site was Vote for the Worst, which was one of the first places to notice the aforementioned trend in the show favoring pop-unfriendly singers — and proceeded to try and reinforce that trend, in the hopes of sabotaging a show that it saw as a blight on the pop culture landscape. The site burst into public consciousness in season 6 when it gave its endorsement to Sanjaya Malakar, and thanks to their efforts and those of others (such as Howard Stern, who promoted the site and interviewed its creator on his show), the Giftedly Bad and otherwise hopeless contestant Malakar made it all the way to the Top 7 before he was eliminated.
When Vote for the Worst bowed out in 2013, its creator stated outright that it was because he felt that the site's work was done when it came to bringing down Idol and eroding its relevance in pop culture, but also noted that the site was merely a culmination of all the rotten trends that had been plaguing the show for years. In addition to serving as a reflection of the show's problems in favoring "white guys with guitars", Vote for the Worst was also a textbook example of a catastrophic, slow-motion failure in managing audience reaction in the age of the internet — the show's producers openly dismissed the site during the height of the show's run, only acknowledging its impact once it became too great to ignore and was seriously affecting voting patterns and the show's reputation.
- This episode of Shark Jumping, meanwhile, while ultimately citing the aforementioned controversy over Kris Allen's victory in season 8 as what sent the show over the shark ramp, also makes the case that it was a victim of its own success, which both destroyed its populist appeal and produced the scourge of Hopeless Auditionees who gave deliberately bad performances in order to get on TV, if only so that people would gawk at them. The show was rooted in the premise that anybody who could sing could audition and potentially become a star, and this was genuinely true in the first few seasons, but as it became a pop culture phenomenon, seriously talented singers started entering the competition... crowding out the merely good singers such that, for anybody who didn't have an amazing voice and/or plenty of training, their only hope of getting on TV was to be So Bad, It's Good. Shark Jumping identifies William Hung's infamous audition in season 3 as the moment that foreshadowed this, as he wound up enjoying a brief, yet brightly-burning, career from his butchering of Ricky Martin's "She Bangs" — which was more success than many of the finalists saw. As the good, but not great, singers found it more difficult to compete, many people saw that they could far more easily become famous by following the path that Hung did, and the show's producers realized that it could get ratings and hype by focusing on the Dreadful Musicians in the audition episodes. Eventually, the novelty wore out and the point-and-laugh audience moved on.