How come in some schools frats dont let guys into parties?

[PhiAlpha05]

What everyone else said. In my undergrad experience, the top tier frats tended to be the worst offenders in this area (one in particular wouldn't even let a brother's non-sorority GF into their parties, despite the fact that she's really attractive). People usually knew which frats were known for being more welcoming and having the best open parties (our "brother frat" for the first few years was one of them). I understand wanting to have a favorable girl/guy ratio in the frat's eyes, but wouldn't inviting guys over for a good time be a great potential recruiting tool? Perhaps some of the guys who enjoyed themselves at the parties might come back and think about rushing...