but of late it's #3 Oregon or #4 USC playing an extremely competitive, highly ranked Utah team.
If the opponent was WSU, CU, ASU or UofA instead of Utah, you'd have half the viewers.
For example, USC-BYU late 2021, only drew about 1.5 million viewers. Even fewer than CU-Utah the previous day. Despite both USC and BYU having more fans than both Utah and CU.
It's much more about how competitive and national draw than strictly fan base.