They are referring to the other 7 teams (outside St Mary's- their's is small but at least they fill it) who have tiny, empty gyms. BYU averages more fans at a BYU-San Diego game than San Diego does, and the same can be said for every other school in the conference outside the two I mentioned.
This hurts the perception of the league, which affects rankings, recruiting, RPI, etc etc. In fact when Mark Few made his comments about wanting the rest of the league to "pull their weight" a few months ago I think that was in reality a more tactful way of criticizing their "high school gyms". Most WCC schools are not as invested in their basketball programs as they could be and it hurts those in the conference (BYU, Gonzaga, St Mary's) who are invested and want to be successful on a national level.