Because all the money and fan support doesn't change the Big 10's primary recruiting pool - the north and east. The talent in this pool doesn't compare to the talent in the deep south and Pacific, and the SEC, Big 12, and Pac 12 own these pools.
It's also why I think Mike Valenti (a guy who does sports talk in Detroit) is absolutely full of ****. He is 100% convinced both Texas and Oklahoma will be playing in the Big 10 within the next 10 years (likely the next 5), because they pay in the Big 10 is much better than the pay in the Big 12. Bull. ****. Maybe the pay is better in the Big 10, but Texas and Oklahoma can play in whichever conference they choose. Both of these schools refuse to play in Ames in November if they can help it because they don't want to play in cold weather. If either school became dissatisfied with the Big 12, why would either team choose to play up north when they would get a similar deal from the ACC, SEC, or Pac 12? But then, the guy is a Michigan St and Big 10 shill, and he also works in an industry where everyone has a voice that comes straight from their ***, so he can say what he will.