It doesn't seem money is really a factor. If he wanted to jump for money he could and, while he's not in the top 20 of coaches salaries, he's not rubbing nickels together. What's a better financial move? Keep a job making $4m a year (avg) over 10 years where they won't fire you for a bad year or get canned in 4 years where you make $5-6m and then can't get picked up again at a major level?
Obviously, don't know the guy, but hearing @Al_4_ISU talk, my guess is what he wants most isn't the highest paycheck, but more where he can do it his way. Can he do that at Michigan, or does he have to do it the Michigan way? Or like FSU, is it a Jimbo battle between what he wants, vs what the boosters want? If the Cyclones can give him a blank slate to do what he wants, how he wants, the job security to not have to be 10 wins a year to keep his job, and the facilities to stay in the race, what does he really gain by moving if he's already prepping to play in championship games?
I know you said Penn State doesn't seem to fit, Al, but for me Ohio State and Michigan don't really fit. Yes, both are blue bloods, midwest, mega money. But if you're not recruiting the 5 stars and running the ship the way they want it run, you're not going to be there long. Neither are really "blue collar" approach jobs. Penn State could be that, basically ISU on steroids.
Either way, wouldn't shock me at all if he ended up at one of those three or ended up doing what @Parliament mentions in being the next Snyder, or Fry, or Ferenz, or Gundy, or Beamer, or Patterson, or Fitzgerald, or Dantonio, or Cutcliffe, etc. None of those guys are in jobs that have significantly more advantages than he has currently, and they all stuck around.