"We're projecting that number to be somewhere between 13 or 14,000 for student ticket numbers this year," Michigan associate athletic director of media and public relations Dave Ablauf said. "(That number was at) about 19,000 last year. We don't have a finalized number (yet), that's just an approximation because all the incoming freshmen haven't put in their orders yet."

http://www.mlive.com/wolverines/index.ssf/2014/05/michigan_football_projecting_s.html

This explains the issues in more detail, and was written before the disaster of a season this year, and before the well publicized coke giveaway debacle:

http://www.thepostgame.com/blog/road-saturday/201406/college-football-fan-stadium-students-business-tv-ncaa-michigan-tickets