My guess is that the answer is geography and I honestly somewhat agree with you on that. They'd be an average of 1200 miles from each school with a high of 1700 miles from Washington and Washington St.

But we need to be consistent in our logic. We all think BYU is an obvious add for the Big 12 when they're an average of 1200 miles from members of the Big 12 (+ one of Houston, UCF, Cincy, Memphis as potential other additions) and nearly 2000 miles from Morgantown, West Virginia.

For the PAC12, you could get that average travel distance for Texas Tech down to 1050 miles by adding K-State, Oklahoma St and TCU. Plus you'd use scheduling to have two largely distinct divisions.
With a West of: Washington, Washington St, Oregon, Oregon St, Cal, Stanford, USC, UCLA
and East of: Arizona, Arizona St, Utah, Colorado, Texas Tech, Oklahoma St, K-State, TCU (also note that I wouldn't be too shocked if BYU or UNLV replaced one of K-State or TCU)

you could set up a schedule of playing the 7 teams in your division every season, and 2 of the 8 in the other division (one home, one away). That would allow you to still have 3 OOC games, to play every team in the conference over a 4 year span and to have (at-most) one long in-conference road trip each season. The longest intra-division travel would be 1150 miles (USC to Washington) or 1200 (Utah to TCU)