The way we play this season is the problem.
We basically have one striker up front, Tevez floats around (and does this job well) but it means that often we have nobody or one player in the box Vidal/Pogba/Marchisio are not making the runs into the box which is adding to the issue.
When Morata comes on he plays well individually but he likes to drift wide meaning that our one player in the box goes down to zero at times.