The answer, I think, can be derived from a coach adhering to one of these two schools of thought:
1. I want to move up as quickly as possible to get my favorite Division I-A power conference or elite school.
2. I want to stay with one team (maybe my alma mater), even if they are in a lower division, and build a dynasty.
There are other motivational factors. I had a great time recently taking a D3 school that had never won a national championship in any world (McMurry) and winning it all in Dobie. But it took me 8 seasons to do it. Not everyone has that level of patience, even in a dynasty game.