If the B12 has 10 teams, there are fans from 10 teams interested in the conference games on TV. If the B12 has 20 teams, there are fans from 20 teams interested in the games. Doesn't the latter lift TV viewership (on average), thus making more money per team? It isn't a linear relationship, but it seems like there would be a significant benefit.
BYU is significantly more valuable in a conference than independence. Aren't the six PAC schools more valuable in the B20 than in the P10? I sure think so. I expect it to happen barring some idiotic arrogance, which is always possible with the PAC.
On a side note - any chance WSU or OSU feel a lot more empathy towards BYU plight the last decade? Sucks to be them for sure.