Why would the Pac 12 become much more attractive? Is it the outlandish travel, no regional rivals, a conference membership that doesn't want them, and less money that makes the PAC 12 more attractive?
Outlandish travel: check
No regional rivals: OU, OSU, TT are regional rivals, plus CU isn't that far away
Pac 12 doesn't want them: They do want Texas, they just don't want the UT/LHN combo
Less money: the Pac 12 is going to be getting WAY more money than the Big 12. I think the Pac 12 will distribute more per school than Texas will get from the Big 12 and the LHN combined.
Texas is in the Big 12 because the Big 12 lets Texas have the LHN. As long as the LHN exists and as long as other conferences are unwilling to allow members to have their own network, Texas will likely remain in the Big 12. If the LHN ceases to exist, Texas will leave the Big 12 as soon as practicable. If the Pac 12 changes its stance on the LHN, Texas will leave the Big 12 as soon as practicable. The Pac 12 is more prestigious academically, which appeals to the University side at UT. The Pac 12 is more stable, which appeals to anyone with a brain. The Pac 12 will very soon be getting much more exposure, which appeals to the Athletics side at UT. And the Pac 12 has more money. The only reason Texas isn't there right now is because they (currently) can't take the LHN with them.