Money being the reason.
But USC and UCLA don't really bring anything sports-wise the B1G. USC football hasn't been like they were when Pete Carrol was there, and I guess UCLA men's basketball, baseball and softball the only sports that compete for titles the most.
I see both USC and ULCA going back to the Pac-12 after a few years when they realize they are never going win in B1G in football.
Can't say to get more views for BTN when that is on every cable and satellite package, plus they never use all the BTN channels the way it is.