could be he's got anxiety/depression/something and he isn't handling millions of fans, the sports media attention, his own organization destroying him 24/7 for months on end and he's just had enough.
that's a lot of pressure.. and, yes, lots of other athletes perform under pressure but everyone is wired differently.
if he's going through the wringer and can't take it.. but he gets traded and things settle down.. then suddenly he performs well, it doesn't mean he tanked in Philadelphia (necessarily). could just mean he found a better fit mentally, emotionally, etc.
i know i mocked his suckiness and think he's over-rated, but i'd never attack the guy personally on Twitter, Facebook, at games, etc. unfortunately there are hundreds of media outlets and millions of other people who have absolutely no problem doing just that and they dngaf if he kills himself because of it.. they'll just label him weak while wearing their green Mental Health Awareness ribbons.