Apologies if this has already been mentioned and I've missed it, but as bad as his diving has been this season I think it's a symptom of some of the rough treatment he got last season. Especially early in the season, he was targeted by opposition players and kicked all over the shop. Usually with very little protection from referees.
I'm absolutely not saying that it's not his fault or that he's not been going to ground pretty pathetically this season. But it wouldn't surprise me if it was at least in part a reaction to the treatment he has been on the receiving end of.