I'm very glad that groups like PyLadies and Women Who Code exist. Unfortunately I'm pretty terrified of meeting men that are significantly more experienced than myself in the industry when it comes to software. I'm terrified of coming off as clueless or air headed. On top of that, the men I have met in the industry are extremely intimidating. I've already had multiple experiences at University where a male peer has looked down at me due to my gender.
This is probably just a simple self confidence issue since I'm young however my point is groups that are women centric are a lot easier to relate to for someone like myself. I love the prospects of meeting other women that can give emotional and professional advice while sharing their work experiences with me. It's much easier to relate to and I'm sure networking with other women makes it easier to transition into the industry from school. Just my two cents.