I think the dude just wants to coach offense and I think he enjoys a challenge. If you look at his historical choices as a coach, none of it has been predictable outside of him going to the NFL. He took over an Oregon program that was down, he took over an awful 49ers team, he took over a UCLA team that had been doing nothing, then went to Ohio State to challenge himself to win a natty.
Seems like he has the mindset of the underdog. Only thing missing from the guy's resume in this context is being OC at an upstart FBS independent.