The simple answer is stability. The Big 12 took their hit, then expanded and have their conference going forward. Nobody is really worried about anyone leaving. Their situation is a relatively healthy one compared to the ACC where no one knows what is going to happen. There may be an ACC in 12 years, there may not. Who will be in it? Who knows. I doubt Clemson and FSU will be the only ones to leave. I would disagree as well on the payouts. It would be pretty surprising if the Big 12 doesn't pass the ACC in payouts, possibly by a good margin, when they renegotiate in 2031.
Like I said earlier, the Big12 currently is what the ACC would be if FSU and Clemson leave. The Twitter trolls who say that the ACC is "in trouble" and "unstable" are just trolls. The ACC is currently what the Big12 was 5 years ago. The Big12 is currently what the ACC would be if all of the "nightmare scenarios" come true.
According to the projections I have seen, the Big12 will not make more than the ACC (per team) until the end of their current contract. With the way TV contracts for sports have been progressing in the past few years, it is also possible that the Big12 will make substantially less money when they negotiate the next TV contract. Nobody knows what the media appetite for sports will be like at that point.
Also, I would not be surprised for the entire conference arrangements and media structures to be turned on their head when athletes are legally declared to be employees. I think there is a decent chance that IF FSU were able to negotiate a buyout of the GOR in a few years and pay $400 million to the ACC, that within a couple of years, the entire conference alignment model would disintegrate. FSU would be out $400 million and in the same situation as the rest of the teams from the ACC, and in the same position they would have been in had they not paid the rest of the ACC any money.
I wasn't there and don't take it as gospel, but I heard/read from a few people that the mood at the ACC football media days was subdued. That it appeared to people that the ACC is dug in for a long court battle, and that FSU is now resigned to wait for a long court battle. I don't think anyone is leaving the ACC anytime soon. (Even though Swaim made a claim that FSU and Clemson would both announce before next Thursday. And then I think he changed it to 8/15/25. And will probably change it again between now and 8/15/25.)