Bronco has a very different personality. He loves the game of football and using the game as a tool for building young men. A lot of the other stuff that necessarily comes with coaching at a high level clearly rubs him the wrong way. NIL only makes it worse.
I think that if he wanted to coach at a power conference school, he could. But at some point, the money they could pay him doesn't buy him what he really wants. At UNM and now USU, he can get paid millions (instead of multiple millions), raise horses, and teach kids. To a guy like Bronco, what more could he want?