Because he's too predictable.
When he does start, he gets figured out after fifteen minutes and gets closed out of the game. He then gets taken off after 70 minutes and we worry about whether he's good enough or not; Blackpool is a good example. He had a great first 10 minutes but after that we didn't see anything from him. However, against Newcastle, he comes on as an impact player and scores. It was the same against Sunderland last season. He's too predictable: he won't go outside and he won't use his right foot, and until he does, he won't be the complete winger we all think he is.