John Cena's gimmick is amazing if you remember that he has always been a robot.
He was a cyborg created to become the top wrestler in the world. First he was sent out as a Prototype with some ability but had not programmed in a personality, so he co-opted Hip Hop culture in order to bring some dynamism and engage people. After that he began to strip away his personality again in order to appeal to the widest audience possible.
At some point after doing this he started to lose supports en masse, which caused a glitch in his programming. This removed much of the very little humanity he had sparked over the years so now he fakes it by donating his time to Make-A-Wish but shunning genuine human contact with his wife and family.
Nowadays his mechanical systems remain as perfect as ever, but his circuity and Artificial Intelligence is badly damaged from all of the beatings over the years. Because of this he can't make coherent thoughts, instead speaking in soundbytes that only contain the themes of overcoming odds, the name of the next pay-per-view, and one piece of dated pop culture at a time.
The next step will be for him to strip away his human flesh and taking back the WWE title giving his internal core an infinite supply of power.