Simply put, it's all about the money and it really got nothing to do with the die-hard fans. Those fans like me and everybody on this board will go a buy anything the WWE does not matter how crappy it is. Everybody in WWE knows that. The real power lies with the casual fans. The families that follow the product on tv. The fans that only goes to WWE show once in a while. These are the people that actually have pull with WWE because these are the peoples that will go and buy a John Cena or C.M Punk shirt. These are the peoples that will cheer for guys like Daniel Bryan And Kane even through the die-hard fans would love to see these 2 break up already.
At the end of the day, the causual fans are the ones that will make the most money for the WWE because they just don't care about who is the better wrestler and how badly a guy is booked. If they like a character they will buy his merchandise no matter what and that's how the WWE was able to survive since Vince Mcmahon bought the company from is dad back in 1983. That's how Hogan was able to stay on top for as long as he did. That's how Bret Hart, Diesel, Undertaker, Shawn Michaels, HHH, Austin And Rock were able to become legends in wrestling, because casual fans actually like them enough to go and buys their merchandises.
So in the end, the only way you would get somebody like John Cena to turn heel would be for all those fans that hate Cena to stop buying is merchandise, outside of that, that the real power of the crowd.