Sorry, the mockery part is really exclusivley to the fans. The guys in the back admire cena because he pretty much has no life outside of WWE.... as weird as that sounds. Nor does he want one.
But the fans? They all see him as a mockery... not because he doesn't enjoy the business, but because he's a bad charicature of the 80s and is terrible at basic fundamentals, things like putting a feud/rivalry over, selling an injury, telling a story in the ring, working the crowd... It's like... like if a magician does nothing to protect the secrets behind his magic while he's performing them. If the audience can see through the charade of what you're doing, it's no longer a performance art. It's just a performance. A dull performance with everything that makes it special sapped away.
If a crowd boos a wrestler, a wrestler is supposed to then begin acting more heelish... to work the crowd and feed off of them, and at the same time allowing the crowd to feed off of their heelish behavior to produce even more boos for them and cheers for their opponents. That's the dynamic crowd/show interaction that makes wrestling "sports entertainment," as opposed to a circus, or a soap opera.
But Cena doesn't work like that. Instead of feeding off the crowd's reactions... he dismisses them, and the reactions get passed off as "controversial" by Cena, by the announcers, and by creative.
If you're taking some time off because of injury, and brock lesnar pulverizes you in a match, you're supposed to sell the beatdown on your way to the back, being carried out by refs, or spending 20 minutes after the cameras finish rolling crawling and stumbling up the ramp on your hands and knees. You don't stand up, thank the crowd, say you'll be going away for a little bit, and walk to the back at a slow pace while holding your arm and feigning a limp while your music blares.
Cena just plain doesn't seem to know how to be a wrestler.