I guess the writing was on the wall. Probably the second worst season of his coaching career, his DC leaves and commits started dropping like flies. Coming off a huge disappointment of a season and an incoming recruiting class ranked in the mid 30's.
Enjoy the rest of your life.
Kind of a bad time for him to decide to do it now though. Who's out there that they can hire at this point, and it pretty well kills any chance for Miami to bolster their lackluster recruiting class on NSD.