They find reasons to hate him because after all of his brilliance tonight, tommorow night he can easily play the exact opposite.
He isnt consistent. If KG, Ray, Pierce were ever as inconsistent as Rondo is currently back when they were the sole superstars of their team, they would be crucified by fans and media.
The Big 3 told Rondo if he wanted to be a superstar he had to bring it every night, unfortunately he hasnt took that to heart yet, hopefully one day he will.