One is our on-court performance, which admittedly has sucked lately and we can't blame that on the conference we play in. But the level of competition (even if we occasionally lose one we have no business losing) and the lack of fan support (which the gym size complaint is really a proxy for) really are grounds for complaint. BYU gets very few chances for Top 100 wins when the conference schedule hits, which was not the case in the MWC, and the lack of fan support ensures a very low level of press coverage in even the good years. A team that has a solid national following and can consistently put 15,000+ butts in the seats at home simply doesn't belong in a conference with a bunch of teams that can't fill gyms a fraction of that size and for whom a sub-200 RPI is pretty much the expectation year in and year out.
We haven't performed up to our potential on the court recently. But if we were, it would make the difference between us and almost all the other teams in the WCC that much more glaring.