In my opinion it's because he is a character that fans love to hate. One of those player's that you love on your team but would hate playing against them.
He is petulant, he gets involved in conflict, he has had prior indiscretions and he has ability.
I think these things mean people like to put the boot in, which I don't mind, but it's when double standards start creeping in and media outlets start over-analysing everything that he does my main issue is with.