Your last question, yes they actually do. Many of those Big12 schools road trip along I35. In fact, nearly every time Texas plays at Iowa State, Tx fans spill over into Minneapolis-Saint Paul. I've asked often enough if they drive. If they're driving to Ames, they're quite likely road tripping to the others, since they are shorter drives.
Austin to Ames can be driven in 14 hours, maybe less. Austin to Seattle, man that's more than a day - you bet I'd be flying - and that's the case for many other Pac12 schools if Tx joined. As for Morgantown, well it's pretty obvious why WVa has been called an island in the Big12 and travel expenses were raised as a huge concern after their first football season.
UConn would certainly have travel issues in the BIG, but at least Rutgers, Md, PSU, OSU and the Michigan schools would fall under 11 hours drive.