From what I heard (and I don't know ) is that the Michigan team was built to win now, and in 2024, its going to need a rebuild. On the roster they had 66 players, 26 of them are freshmen and sophomores, the majority are junior and seniors. Their defense is similar, in that they 69 people on defensive roster, 38 are freshmen and sophomores.
To me, I think his departure was a done deal regardless of the national championship win. I think with the NCAA breaking down Michigan's neck, how the administration has hung him out to dry, and no backed him up, left a bad taste in his mouth. Also don't forget a few years back, they gave him an ultimatum - take a massive pay cut or get fired. He said all of the right things, but you don't forget that.