ratio

Why are there so many fraternities compared to sororities when 3 times as many girls come out to rush compared to guys? A good class for guys is like 10 depending on the semester, while girls will likely take 30+ sometimes. With a majority of the school being girls, shouldn't they have more organizations?
Fraternities - 10 with 2 more up and coming.
Sororities - 7 with 0 up and coming(At least to my knowledge).