It's hard to put your finger on exactly how it's got to this. Other ex-players don't seem to get the same level of stick.
I imagine the frustration and anger, both from him and his family, over not being signed by FC and putting it out there probably didn't help.
His behaviour in some games won't have helped either.
It's actually quite sad, and I imagine it's tough for him.
The best thing he can do is knuckle down, show a bit of humility, avoid playing up to the crowd, and hopefully the idiots will eventually get off his back.