The NFL is tough. Its tough to find a situation that works best for your talent. No coach has won a SB with two different teams.
He goes into Miami, a team with a recruiting base thats as good as anywhere, a team with history on its side, and a sellable location.
Yelling at players in the NFL only gets you so far, some respond but alot dont. In college they more often than not do. Also his age helps with recruits as does that SB ring, and his visibility with players since he was on ESPN during the ftball season. He has an in with every ftball star that way.