re: I still don't understand why coaches have any say in the 8 vs. 9 debate

Mainly because the input of the people who know the most about the sport, regardless of their biases, makes perfect sense, I'd say. You don't ask the presidents to call plays on the field and you don't ask the coaches to debate academic departmental funding, but it's always wise to ask the coaches about matters related to football, especially since football is a huge revenue sport and the coaches can offer insight into the best way to succeed. Yeah, they're going to want an easier path...unless, for instance, they want a harder path with greater chances at better dividends.

The presidents and ADs don't have to take the advice of the coaches, but they certainly should listen to them.