I,personally,believe that 99% of lesbians are that way because no man would be desperate enough to get within 50 yards of them.
Not sure I’d put the number as high as 99% but it’s definitely high. It’s difficult to know what’s really going on in someone else’s mind, but I do strongly suspect that a fair number of lesbians aren’t really turned on by women. They are, as you say, shunned by men, and turn to lesbianism by default. Any port in a storm, as the saying goes. With that said, I’ve known a large number of “lipstick lesbians” in San Francisco who are attractive, even beautiful, and who could certainly date men if they were so inclined. For those girls, obviously something different is going on. I suspect that for at least some of them, there’s been some sort of past trauma with men that drove them into the dyke camp. In a few cases, lesbianism didn’t “stick.” One girl I knew who was dating women 15 years ago is now married to a genuine man.