Guessing they see him as a winger and there's zero minutes for him. I really wouldn't mind him up top at all. It would easily work in Ancelotti's system, most of the time he uses a false 9 anyway.
Reus is one of those rare player that can thrive as a true 9, winger, or CAM. He's got such versatility, which is why I think he's such a great player. He also has hair to rival Ronaldo and Bale.