Because he's BLACK!
Actually, because of three reasons (to steal from GunnerBill)...
1 - Communication - he's terrible at it, specifically to the media (public speaking), absolutely nothing to do with skin color
2 - Leadership qualities - no evidence that he had much of them, considering he was such a nervous nelly in front of the media, absolutely nothing to do with skin color
3 - Vision - Maybe this was effected by lack of coaching staff stability, but I don't think so. Trading up for Sammy was proof that he didn't have much vision, if any - again, absolutely nothing to do with skin color