Personally, I like John Cena the man but hate John Cena the character. What Cena says about the Rock... whether you want to admit it or not, it's all true. Cena (and many fans, myself included) feel the Rock really weaseled and wormed his way out of the business. He would take some time off for a movie, come back, wrestle a pretty limited schedule, and go shoot another movie and maybe make an appearance if his schedule from the movie allowed it. Then the Rock would show up at these total random moments on Raw that continued to really tease the fans. I personally loved when he showed up to side with Eugene, his appearance in the Diva Search, amongst a few others. But he kept coming back and each time back, you forget how much you really missed The Rock. So all these random appearances, obviously to a fan not really "in the know" at the time, really gave the sense that he would come back sooner or later. Then... the appearances stopped and it was very public that he said he was no longer under contract with the WWE. So again in a sense, the Rock was teasing us. But you also have to ask yourself, would you rather not have those hilarious random moments at all? I know I enjoyed them and glad he did them.
Why are most of us bitter though? I think we're still bitter with The Rock because we never really got a "final appearance" or a final match. When The Rock/Hogan match was over, Hogan passed the torch to one of the faces of the next generation of wrestling. But what'd The Rock do? In 2-3 years, The Rock was essentially done. We never knew that a certain appearance would be his last and as fans, we were all caught totally off guard. Looking back, do I expect a send-off like we gave Ric Flair on Raw after WM24? No. But let us know. Let us brace ourselves for the final appearance. Have a "retirement" angle or episode of Raw or something. ANYTHING!!! That's why us fans are bitter in my eyes.
Cena's reason could be a little of the same but also different. We all know we've heard time after time how much The Rock loves the business, his passion for the business, etc... But yet, he just up and left the business that he "loved." He did it for Hollywood. Was the WWE not a big enough stage for The Rock? Cena's right. If you have THAT MUCH passion and love for something, you can't just up and leave the way The Rock did. It's impossible to walk away from something you love that much.
Cena also juggles his schedule with the WWE and movies and claims that he would never leave the WWE for Hollywood the way The Rock did...or at all for that matter. Cena loves the business and the fans just as much as The Rock does/did. But The Rock left us all hanging. It's tough to swallow for the fans, the other guys in the back, and for Cena who is pretty much following the same path with wrestling and movies.
You have to look at both sides. Should we be happy with the time The Rock entertained the millions... AND MILLIONS of The Rock's fans? Yes we should. It's better to have those memories of such a memorable superstar than to just be bitter about it the whole time. But do we have a right to be bitter? Yes. No matter how you slice it, The Rock really did kinda just... go. He up and left and nobody really saw it coming. We all thought this movie thing was a "side-life" if you want to call it that or a side-project in the game of life...whatever. But it wasn't. We're unhappy with the way The Rock went out, Cena's unhappy with the way The Rock went out. We have that right.
I think it would be interesting if somehow we could draw up a petition and have everybody that is drawn to The Rock's movies sign this petition and vow to never pay a dollar to see his films until he steps back into the ring. See how much the Hollywood life suits him then when nobody will see his movies. Not that it could ever really happen, but it would just be interesting to see how it would play out if it could.