why is sae so exclusive?

Yeah, i get it, SAE is the top house, but why are they so mean to girls not in sororities/top houses? like all the girls they let in are either AXO, APhi, or PiPhi. The guys literally quiz girls at the door about what sorority theyre in and who they are. I mean, I've seen plenty of really really pretty girls not in sororities, but are SAE guys really not gonna let them in just cause theyre not in a top house/not greek? (<--- thats a legitmate question, btw.) It makes me so mad and upset seeing girls judged off of if they're in a top house or not.