Put very simply, because it's been talked about loads, it's because he left in January when we were in the middle of a relegation battle, instead of seeing that out and then leaving in the summer. The way he went about getting a move got a lot of peoples backs up too. Being out with a phantom injury to force the club's hand.
The fact that a couple of weeks before the transfer window opened he reckoned he was happy at Newcastle too.
He's certainly not the first person, or the last to do that.