For all the talk of expanding to the East, I suspect the University presidents are more comfortable with extending their perimeter. Hence, Colorado (the worst PAC football team, but an old member that was good under one coach three decades ago) and perhaps Arizona (who as you say is far from a power).
The problem they have to face is why is the Pac12 so unpopular with networks? Colorado is mountain time zone. Arizona is pacific.
This matters to the networks a great deal.
When you look at what the Pac12 had in terms of brand name schools, I would pick the brands in the P12 over the B12 leftovers.
So why is the Pac12 worth so little?
This matters a lot to the decision makers.
There's a problem with the west coast.