I agree leaving the B1G for Louisville doesn’t make a lot of sense but it could depend on the size of your ego
In other words does Brohm feel he can make Louisville good enough to eventually join the SEC?
I think the one thing other than it being his alma mater that could sway Brohm to Louisville is that the path to the playoff is much easier. It is definitely possible for Louisville to win the ACC or make it in the top two to qualify for a 12 team playoff. Sure there are a number of teams that have a better foundation to run the ACC. But I'd put Louisville just in the top half of the league.
At Purdue, will they ever make the playoff? I do not think they are capable of getting there in a divisionless B1G with Ohio State, Michigan, Penn State, USC, Wisconsin, and Michigan State ahead of them.
So if his priorities include having a nationally relevant program, with the upside of it being your alma mater, I think he could make the move. If he is asking what job will I be most comfortable at for the long run, then he probably stays.