Cena was never about "what the fans wanted".....he was boo'd for half of his run & he had the most boring run until The Rock stuff, after The Rock when they stopped mega-pushing him & started putting him in the undercards, gave him the US title, he started feuding with new younger talent, then the "other half" of the audience started to appreciate him more. But don't pretend WWE fans weren't booing this man for a decade of his career, from like 2007-2014 this man was the most hated man in WWE. There's a reason why Punk's (then Bryan's) ascension to the main event was such a big deal because everyone was so tired of guys like Cena (and to a lesser extent Orton & HHH) being the only real main eventers for YEARS
Good summary of Cena's run.
I can't stress enough that the IWC (hate that term) from that era never hated Cena, we just wanted better writing for him other than "destroy the roster, win belt". and it took years until we got that. The general consensus before was that Cena was refreshing. "Word Life" wigger Cena was fun and that was the guy we wanted to see. Vince took a liking to him and changed nearly everything we loved about the guy and just made him a generic good guy.
Cena's run is an unfortunate achievement in that he is the first successful WWE-only guy. A realization of everything Vince envisioned - A guy 100% born and bred in the WWE system to serve only the WWE system. No mystery, no surprise, just one style, one setting his entire run as sterile and manufactured as possible. You could argue The Rock to a lesser extent, but if Rock hadn't come in the late 90s in an era where Vince was desperate and throwing things at the wall, he wouldn't have became "The Rock".
Hogan, Flair, Austin, Foley went other places, and added to their character and body of work and that's a lot of why they became so much more beloved. Cena's entire legacy feels manufactured with no opprotunity to grow and become more than what he was. We never got Cena in NJPW or AAA, we never got Indie-Cena. A hugh missed opprotunity for Cena and ultimately, the fans.
This is why Roman Reigns got such a violent reaction whenever it was made clear he was the next guy in line. As a wrestling fan, I want this system dead.