It's more than just money. It's culture.
The PAC 12 is academically superior to the Big 12. It's head-and-shoulders above the Big 12 in research.
A large proportion of USA Olympians and medal winners come from the PAC 12 become the conference focuses on Olympic sports; the Big 12 focus is elsewhere.
There are reason that in 2010/11, even after TAMU and TX had declined joining the PAC 12, that Boren still wanted OU/OSU to be invited.
The Big 12 has not been attractive to any other power conference team, since WVU became a member. And there is reason for that. Many expect OU and TX to leave when the GOR expires.