If you want to go deeper, it's really because of Title IX. Schools that receive federal money, which is basically every school including private, have to have the same amount of male athletes as female athletes or they may lose funding.
Because there's no real female equivalent for football with its huge rosters, that makes fringe sports get less full-ride scholarships or get cut on the men's side like volleyball, tennis, gymnastics, and even wrestling. It's actually why we dominate a lot of women's sports around the world since other countries don't fund women's sports as much.
So yeah it's about popularity but even dudes who are interested in volleyball have to deal with the lack of support.
and the crazy thing is for these women and even men to make proper coin in volleyball, handball and these other sports that americans dont watch etc. is to go overseas. Even women soccer you'll make much more playing for the women arsenal, real madrid, etc. than you would playing for NWSL except for a select few