Part of the problem is that many lesbians are lesbians because they are very uncomfortable around men, perhaps due to bad experiences in their younger days. One lesbian I knew told about being molested as a girl by her dad and his friends.
Thus, a lot of lesbians are accepting of biological men, however the men identify. This makes them politically incorrect.
Also, women who don’t usually have sex with men, are unlikely to be on birth control, and thus more likely to get pregnant when they finally have sex with a guy.
Correction: NOT accepting of biological males.
One of those explanations that seems really obvious once someone says it. LOL!