Back in the day, there were few to no release rules and some groups would keep as many girls around as possible for "eye candy", then do massive cuts before prefs--where there were usually required numbers. For instance, some schools required that your pref party numbers be no more than 1 1/2 to 2 times the numbers of bids that could be handed out. This was also aided by the fact that at many schools, quota was determined early on; they might take the number of girls still in after first parties and divide it by the number of sororities. Both of these led to the big groups staying big and the smaller ones staying smaller-or folding.
I think we hear more about the cuts from selective schools like UGa because you have to be so outstanding to get in now. Certainly no freshmen are cut for grades and I have no idea how the heck the sororities are able to manage the giant cuts. Anyway, the women who are rushing have been rejected very little in their lives; they've accomplished so much and when these outstanding women get cut by 75% of the sororities after second parties, many, many drop out. Unless someone personally knows some of the outstanding PNMs who get cut (like, say, the women whom NUBlue&Blue knew last fall) they can not begin to imagine how fabulous these "recruitment dropouts" are.