Just an opinion:
I think the real powers that be know they cannot completely disassociate with everyone. They need bottom feeders to elevate the powers and almost powers. In a close system, there are only so many wins available. Half will win, half will lose each game.
By separating select schools they eliminate playing lesser divisions and they alienate the fanbases. Sure, I may watch a game here and there in the new super league, but I will not waste a full Saturday on teams I could not care about unless they played SU. People have lives to live, CFB, as enjoyable as it is, is not my life. Besides, does anyone care about Mississippi State v. Minnesota?
Anyway, if schools outright pay players, most colleges cannot join that super league. Further, the rivalries and traditions will become moot. Those are selling pints and have been largely watered down over the past three decades. Further erosion of tradition and rivalries drives fans away.
In the end, I thing the SEC and B1G want the FBS together sol long as they get the lion's share of the take.