Plus, I don't think it's fair to call Pete Carrol a terrible NFL coach. He was elite or anything, but he wasn't a joke. Plus, he was a lot younger, maybe he's learned since then...maybe he relates better to the college game.
In many ways Carrol's legacy never had decent shot. He is sandwiched between two of greatest coaches ever -- Parcels & Belichick.
Also lots of folks do a better job when given a second shot. Belichick didn't rackup Canton type qualifications in Cleveland. Norv Turners best season was his 10th with his third team. Etc.