Many Pac fans didn't want expansion period. They are a stable conference, and have been a constant since the Arizona schools. Every other power conference has either added or lost teams since the Arizona schools were added to the Pac. So it has had the least amount of movement, and fans liked the conference as is.
Now with the Big 12, they are falling apart, and desperately need additional schools to keep that ragtag conference that no one wants to be a part of together. Even in that environment, the fans are not stoked about BYU.