Probably because their fans blew all their money on non-refundable trips to Indianapolis!

https://www.freep.com/story/sports/college/university-michigan/wolverines/2018/12/22/michigan-has-sold-63-percent-its-peach-bowl-ticket-allotment/2397103002/

63 - 39...Go Bucks, and Merry Christmas 11w!