I think Mark Richt had a heart-to-heart with his wife, his family and leaned on his faith for a big time decision.
Fact is, he was set to retire three years ago when Georgia let him go—but took the Miami gig because it was his alma mater.
Probably had a five-year timeline and thought he'd be further along entering year four. Instead, year three was his worst as a hard coach since 2010.
The thought of having to gut his staff, give up play calling, dig in harder / work harder for a rebuild—and extending the timeline in doing so—realized it made sense to tap out now and let someone younger and hungrier come in to do that job.
Said it after the game—35-3 was a blessing in disguise as eking out a 20-17 loss to Wisconsin would've have moved the needled. Richt was in over his head—in regards to how much work he thought it would take. Toss in the dissension in the locker room; probably feels the game was getting away from him and wanted to focus his energies on family, faith and missionary work he spoke of years back.
Gave Miami the easy out, too—as this thing was going to be a mess late next season if the Canes were still struggling.