"exceptions" (as you see them) are such because of reasons independent of conference affiliation. BYU is in that position because they have recruiting pipelines that transcend conference affiliations.
Factors (non-exaustive):
Coaching
Tradition
Tourney success
Religion
There are only 2 programs in the Pac 10 that have any of these: UCLA and Ariona. Utah had a great coach (depending on your standards), but otherwise lacks any significant draw right now other than playing time against mediocre Pac 10 competition.