it's $$$$$ and recruiting, and the big 12 doesn't matter. by going east, or southeast, they aren't going to open
up any legit recruiting territory. kids in the SE aren't going to go anywhere but their own state, or the SEC. by going west, you open up more recruiting opportunities by instantly being a player to the 40 million population found in california alone.
they also instantly become a player in the PAC, with more say in things than they would ever have in the SEC. the SEC isn't going to bow down to them like the PAC would. that brings $$$$$.