It's just classic mismanagement. He doesn't get into the starting lineups, and sometimes doesn't make it onto the pitch. When he does make it on, it's only for a few minutes. When he does make it on, it's debatable whether or not Ole is putting him in the right position. A lot of people are saying he should be played further back, which I agree with.
He could have had an amazing 10 minutes and he would still be on the bench for the next game. I think we're underestimating just how tricky it is to come on so late on into a game and have an impact. Some players thrive on that, especially if you're a striker running at a tired defence or coming on to get a goal when you're 1-0 down. In other cases, it doesn't always work out that way.