This is pure conjecture so be warned that I have no idea what I'm talking about but it seems like the last 15+ years or so were a period in which college football had massive changes mostly related to money and ballooning pay packages of TV deals. Certain conferences saw the landscape changing and realized that they needed to jump in with both feet and start taking advantage of everything this new era had to offer. Conference brass combined with university presidents in the SEC and Big 10 were just way better at navigating the changes than the rest of the conferences. Not sure why but it's clear the Larry Scott and our conference presidents just didn't have the sense of urgency that the Big 10 and SEC had.
Big 10 and SEC jumped out to a early and sizable lead and just kept leveraging their position to gain a bigger and bigger advantage. It probably helped that those conferences were the most relevant from the standpoint of the quality of their teams over the last 15 years as well. The Pac 12 was fucking abysmal during that period. ESPN and the like didn't really "need" the Pac 12 and they still don't.
Someone has to play the late games. You’re right though, they don’t need the pac 12 to do it. They just need a handful of west coast teams with decent markets regardless of what conference they’re in. This may be the only thing saving udub/oregon. If they go to the big 10, the big 12 has a lot of motivation to get west coast teams to fill that void, otherwise they can’t compete with fox for the same time slot.
Pac-12 after dark did more harm than good, as it became what the networks only Wanted the conference for, but don't Need and with that the revenue or lack thereof that comes with it.
Espn has their lowball number which allows them to make a (+) profit if the Pac accepts, and if they don't, they will fill that window with MWC games. 10-11 pm on the east coast when those game kick isn't a needle mover one way or the other