As I've said many a time, it's up to the player to show it in training. We have no idea what the guy is showing in training .. although, we can get an inkling, given that he didn't cover himself in glory in Dortmund either. For me, he has talent, but I think it's being overstated by some of his bigger fans on here. I think it's becoming pretty clear that he has some form of attitude problem, which hopefully he can get rid of, and go on to use his talents.
Why shouldn't he be on the bench if he's not performing in training? He was given a chance at the start of the season and he wasn't exactly outstanding. Yes, after that he was moved around a bit. At the same time, it's up to him to prove his worth. He hasn't.
Not the manager's fault in my opinion. All on the player. Van Gaal has proven that he will play youngsters, regardless of age etc, if they display that they deserve it. He's made many sticks, our Louis. "Ruining" Januzaj is not one of them.