Since the PAC-12 has 12 teams, who are you excluding in this analysis? There aren't just "10 teams."
I also think your analysis is taking a pretty ungenerous view of things. A more reasonable explanation is that there just aren't as many D1 teams out west - even Stanford has some really soft OOC games every year against the Eastern Washington, San Jose St., San Francisco, UC Davis, etc., types, simply because it's hard to get enough games against (relatively) local OOC competition. But I can assure you Tara is not a "load up on cupcakes" type. I can't speak for every other coach, but my general view is that Stanford, Oregon, Oregon State, UCLA, Arizona St., and Washington St. have all historically sought out strong OOC games, but it's hard to fill out a 12-13 game schedule with them.
I think the part of college basketball that casual fans least appreciate is the difficulties entailed in scheduling - it's a logistical nightmare that involves a ton of moving pieces, costs, and constraints. Just fitting all the other schools into a calendar is hard enough alone, let alone logistics, budget, travel times (and modes), class & NCAA restrictions, etc. There's a Kelly Graves interview somewhere where he talks about how it's far and away his least favorite part of the job, and how much of a hassle it is (and note that Oregon probably has at most 4-5 plausible schools they can schedule OOC games with that don't require a flight). And really easy to critique on the sidelines when, in the end, for any number of reasons beyond a team's control, a team's OOC schedule isn't as strong as would be preferred.
ETA: It's also worth noting how much harder it is to schedule good OOC competition in the PAC-12 - every single away game against another P5 school is in a different time zone, whereas Duke/UNC and South Carolina, or Texas A&M and Texas, Iowa & Iowa St., Kentucky & Louisville, etc., can also schedule strong OOC games with just a short bus ride. Which also means you can have so-so Q2/Q3 South Carolina-Clemson, Notre Dame-Ohio St., Florida St.-Florida, etc. without much travel.
By comparison, Washington St. to Miami, Oregon to UConn, and Stanford to Tennessee are 2-3 time zone games requiring cross country flights and often 9 or 10 a.m. body-clock start times.