The article is addressing multiple issues at the same time. I think ochoopsfan correctly raises the point that there are a lot of sports for the player to choose from; volleyball (beach and court) and softball are staples of southern Cal, of course, and I have noticed the inroads of Lacrosse, really a New England sport originally, out west. And I recently noted the top soccer school was UCLA at the time.
As to attendance, I do think the writer nails issues of big city, multiple choice circumstances. On the college level, one factor could be how the men's programs are doing (or are viewed). In the PAC, it is very difficult to attend both sides as one would be generally attending 2 games per week - not to mention Volleyball and Football ending up as the season begins and softball (and baseball) starting up as the season winds down - we have walked from the softball stadium to the arena several times just following the women.
And finally, there really is a disconnect I think between the west coast and the rest of the country as to college sports. We mostly play other teams from the western part of the country (for cost reasons), just as the teams not west of the Rockies tend to play each other more-so than looking for competition further west. This most likely has an impact as well.