PAC12 schools are stuck in Metropolitan areas which means there are a lot of other distractions competing for fan interest.
Seattle, Phoenix, LA, Bay Area, Salt Lake....these aren't traditional college towns like we see in Provo where everything circles around the University. Look at the Utes.....remember 2 years ago how pathetic their BBALL attendance was? Or why their stadium is smaller despite being in a city? If they aren't winning nobody is showing up. Too many other things to do. Fan attention is very demanding in Commuter schools.