BSU's home games are pretty much the MWC, BYU on occasion, and not much else.
In part because BSU has been dominant, fans don't seem super interested in showing up at odd hours to watch BSU play MWC foes. You see big empty sections there even with BSU is ranked.
BYU has the same thing going on with home games against bad competition. People might watch at home, but going to those games when they are at night or on a weekday just isn't very appealing.