As said before, eyeballs bring dollars. Choosing conference members based on success is a risky short term strategy.
To be shrewd, a truly successful but controversial strategic merger between PAC12 and BIG12, would means culling the smaller schools. The revenue dilution between so many schools make competing with BIG and SEC difficult at best.
(My controversial opinion) assuming contracts even allow would be to drop these to compete.
Wash State, Oregon St., Arizona, TCU, KSU, WV...cal?....and yes Stanford (who cant half fill a 40K stadium).
Perhaps my list is 20 degrees off kilter, but I think something has to give from both conferences for this merger to work.