nation (and was #1 last year):
https://sports.usatoday.com/ncaa/finances/
A&M is academically prestigious in terms of its endowment, research, AAU status, and national rankings.
They have an enormous alumni base, fan base, and one of the best brands in college sports since joining the SEC.
There are only a handful of schools in the nation as valuable as A&M to a conference.
oSu on the other hand is complete garbage (especially now that T Boone is gone). No one wants them.
And OU is tied to them politically by the Oklahoma state legislature. Another key difference is that if OU leaves the Big 12 without oSu, then oSu is SCREWED. The OK state legislature would not allow that to happen unless absolutely necessary. For example, if the Big12 is no longer a viable power conference due to Texas leaving (which is never going to happen).