I don't think it's coming off far-fetched because it's straight girls so much as it's just so MANY girls. No offense, but you kind of make yourself look...hmmm, easy, to put it mildly.
The straight girl/gay girl thing is nothing new. Someone is posting here every day and every night with that kind of stuff. In your situation, I'm wondering if you're femme-looking, and also maybe where it is you're hanging out. It's possible some of these girls are not totally straight, and college age is definitely a time of curiosity and sexual exploration for a lot of people. And straight people who give the appearance of being open-minded about lesbians seem to almost universally prefer femme-looking lesbians as far as social acceptance. Some girls will go after a more masculine lesbian, mainly because these girls are obviously lesbians. But you also said you're fully out, which will spark a girl's curiosity just the same as "looking like a lesbian" will. The double sword to that is that lesbians look right past you--if you're femme-looking, they either don't know or don't believe sometimes that you're really a lesbian. Straight girls will not question it as much. Also, making out and/or hanging out with straight girls all the time could also give the appearance to lesbians that you're not truly a lesbian, whether that's right or wrong. It might make you seem more like a "lesbian until graduation" or experimentation type of lesbian, just like many of the girls you're talking about hooking up with seem to be.
My advice if you want something more real is 1) Quit being so easy. Just because a chick is interested in you doesn't mean you have to make out or sleep with her. And you don't have to do anything with anybody right away, either, and not every chick is interested in doing anything right away. Exercise more self-control, and give lesbians you meet more time to get to know you and become interested in you; 2) Hang out in predominantly LGBT places more often, especially places that have a lot of lesbians.