They don't like him (his wrestling character, not the person) so they boo and voice their disapproval. Just like Arrow fans didn't like Felicity so they voiced their disapproval (very loudly I might add).
What did Arrow do? They changed Felicity's character and made her more likeable, they listened to the fans because that's what a damn TV show should do
Lost brought in Nikki and Paulo, they were universally hated and they were killed off 6 episodes later. Ben was only supposed to be in a few episodes, he ended up being hugely over and stayed till the end. They listened to the fans, I don't get why WWE can't do the same, at the end of the day it's not sport it's just a TV show