Think about it; no matter what he does, what promos he cuts, how many new ways he tries to innovate his move set, some of you guys still can't stand him! The ones who keep begging and begging for a Cena heel turn, to turn his back in the fans have been living with exactly that for years. Since I'm sure that some of you hold yourselves in high regard, despite not being the target demographic, you'd consider yourselves to be of top priority and someone that should be acknowledged. Well, you are. He's a heel just like you want him. Even the most innocuous things he does draws ire from the sandy pits...er...cauldrons of your soul and transforms it into absolute disdain. You'd even go as far as buying Anti-Cena merch, that he most likely won't see, just to tell the world that you're not recruited in the Cenation.
You've had the most brilliant heel right under your noses and you haven't even realized it, have you? Why should he turn heel if he's already there? You're not giving him any reason to change.