They're in the WCC.
5 P12 teams were seeded. That means in the minds of the committee, the 5th-best P12 team was better than the WCC champion.
Here's the breakdown by conference:
P12--5 teams seeded
B10--4
B12--2
SEC--2
ACC--2
MWC--1--Colorado St, who beat BYU early in the year.