What a lot of other posters have said is totally dead on. It's all about how you get your name out there. I was part of a local and not all fraternities on campus wanted to have a social with us. Some did have issues with our numbers (we were never bigger than 30 while I was active and some of our fraternities could push like 80 guys), others just had an issue with the fact that we were local. I thought it was crazy but whatever, to each their own. Go with the groups that want to socialize with you. We had socials with the rugby team and with NPHC fraternities. It helped get our name out there and helped us with some IFC groups. Eventually we could compile a decent social calender. We had some groups that loved hanging out with us and would book us as often as they could. Some would never give us the time of day and it didn't matter how cool other groups said about us. But it will take time. Just be patient and remember, you and your sisters are great no matter what some groups say! Just think of it as their loss!
And even though socials are nice in the end, it's all about the sisterhood and the good works that you do!