Jake has been the heart and soul of the offense, and the coaches likely felt he was good enough to go. Bohannan is a great backup, but it was just as big of a gamble since he had not played meaningful minutes in a long time.
When Jake hurt his left wrist, on the play where he jumped for extra yardage and came down awkwardly, I really thought he had broken it. Then, he ran another qb sneak for a 1st down. He injured that left arm in an earlier game, as well, and played through it to a win, so I imagine the coaches thought he was going to do the same thing.