Why doesn't Cena just turn heel? Sure if he turns heel he will still have haters but he will at least he will have a lot less haters.
Two reasons. First if he had less haters as a heel they'd have to turn him face. You're a failure of a heel if you don't have haters. Second WWE has the impression (right or wrong they don't open their books to me) that heels don't sell merchandise so the number one merchandise pusher is not turning heel. Third they've got something rather unique with him, sure he has haters but haters who come to boo him and if he's putting butts in seats that's all WWE cares about. If suddenly fans decided they were boycotting shows where Cena was the Main Event or if Cena coming to the ring was time for a bathroom break and not a battle between the lovers and haters for who could get the loudest WWE would change something.
Also, if he turned heel, that would break the heart of just about every Make a Wish kid he's ever helped. Nobody wants that.
Why and when did Cena start getting hate? I don't get why he gets hated, can someone tell me?
John Cena got popular with his "doctor of thuganomics" gimmick and fans were asking why WWE did not seem to trust him with a title despite how over he was. He won the United States championship, people were happy. His match with the Big Show to win it was not a real crowd pleaser but they liked John Cena's gimmick and were glad he allowed Big Show to go for the "more important" WWE championship. Brock Lesnar left wrestling to play football, fans were angry with Lesnar but Eddie Guerrero was finally champ so they were kind of placated. Then Eddy feuded with JBL, who fans hated as a main eventer and eventually dropped the title. Fans hated JBL even more as champion and had high hopes for John Cena, he was all but guaranteed to take JBL's title at Wrestlemania. Well, the match was not much of a crowd pleaser, again, so after two wrestlemanias in a row it started to become apparent John Cena was more gimmick than good wrestler, unworthy of the so important WWE championship...but they still liked the gimmick. Then he moved to Raw and the gimmick got gradually worn down to the point John Cena was speaking with his real accent, not rapping and eventually developed an inferiority complex. His matches also became increasingly formulaic. He lasted through Hassan, Christian, Carilto and Jericho but when he feuded with Kurt Angle the fans decided enough was enough, Cena sucked and they were sick of him.
The audience was already angry and hostile before John Cena was propped up in an attempt to placate them. It has not worked as he is not considered "main event caliber" and furthermore what little they liked about him (gimmick, promos, some creativity in spots) were all watered down to near nonexistence (he became a man in shorts who despite being built like a tank could be knocked around as if he was less dense than air but would, without warning, transform into Superman and win with his finishing sequence, as if he was just pretending to be hurt during the ten minute torture session earlier endured). WWE apparently thinks there are enough people who still like him enough to not have John Cena change anything he does or push anyone else in the main event for any comparable amount of time (so in addition to people not liking John Cena, there are those who do like him but hate the way the company is run and hate how he is used). His giant chin is on nearly everything WWE puts out, he is always in the main event, he cannot lose cleanly, in fact rarely loses at all and apparently can do no wrong.
Basically when he started getting pushed to the moon.