The main problems with pro sports are, ultimately you 'go to war with the army you have', and no amount of coaching can change the budget of the team or injuries etc, and of course the B) on this is, the owner can't be fired. It's the owner making the coaching personnel decisions.
A GM usually gives a field manager 3-5 years, then another and another. An owner usually gives a GM 3-5 managers, then another and another. After 3-5 GMs and no success, it’s reasonable to conclude that the owner is the problem. E.g., see Gene Autry of the Angels, Tom Yawkey of the Red Sox, Phil Wrigley of the Cubs, etc. etc. etc. etc.