Why is it that most NFL coaches get fired, always land on their feet on some other team?
They obvious didn't work out, then they go to another team and that team thinks they're the second coming of Christ.
Like a QB, often times coaches land in bad situations (bad ownership, bad GM selecting players, etc.).
Bill Belichick, Pete Carroll, Gary Kubiak, Tony Dungy, Andy Reid, and Jon Gruden all failed to win a Super Bowl with their first team but then got "recycled" and won the trophy with a subsequent team.
The list would grow if the list you include coaches that did even better with their second team but failed to win the Lombardi.
I'm sure that most of us can admit that we learned from each job that we've had, and coaches are no different. Sometimes they need to get fired before they figure out how to be an even better coach.
Conversely it can be risky to hire someone that has no head coaching experience.