I think a have-not halting the process makes sense if it's fearful that the 2 most likely outcomes are continuing being a have-not OR something worse.
Right now, if we say their focus is the SEC, they may get 1 ACC team in a 4-team playoff vs 2 from the SEC. Unequal, but it's the reality. An expanded, 12-team playoff? They may still only get 1 ACC team in vs 4 or 5 or 6 SEC teams. They're then below their current have-not status. Not optimal for them.
Basically if 2/3 of the potential outcomes don't improve their status, yeah, it makes sense to throw a wrench into it.