Location. Since UB went D1, no G5 north of the Mason-Dixon has been offered, accepted, and played a football game in a P5 conference. The southeast is filled with D1 schools that can play musical chairs. It doesn't make sense for UB to lose the location advantage (cost, fan experience of going to away games) and jump out of the MAC into one of those conferences.
I hate being in a conference that has a bunch of failing glorified community colleges, but right now it's the only thing we can do. In the future we can hope the ACC falls apart, which will probably leave the northeast schools left out of the SEC/Big Ten. If they raid the AAC or other conferences we want to be at the top of the list with schools like Temple, even UMass. If they look south (App State, Georgia Southern, ECU, etc) like the AAC is doing, we get left out. We aren't getting there with our current stadium though.