The other conferences have no leverage

Football drives these decisions.

If it wasn't, Kansas would have been on the first bus out of the B12, not stuck despite multiple rounds of realignment affecting the B12.

Even assuming basketball mattered, while I don't disagree that a B1G/SEC basketball tournament won't be some massive draw, the NCAA tournament would take an enormous financial hit if the B1G and SEC weren't in it.

However the other schools have no leverage in football. If the B1G and SEC entered in some alternate format where their champs played every year that would effectively relegate the rest of college football to a step above G5 status. The few remaining schools that are attractive to those two leagues would likely immediately bolt further cementing the leftovers in the ACC and B12 as second tier.