That's a good point. There indeed are some which exhibit this behavior, but that's not their main purpose. the purpose is to create networks. the same with black fraternities. They create networks for their members to plug into.
Yes, we know many of them engage in peripheral racist and misogynistic behavior, but those things are sideshows.
My point is forming these groups which foment cohesion and support for their members are rather common across cultures so to paint them as 'old boys's' networks is a misunderstanding of human nature.
Basically networks may be used to keep the other out --but that's not why or how they are formed. They are formed out of human nature to form groups which help their members --not that different from community groups, or PTAs, etc.