The terms “gay” and “homosexual” aren’t technically gendered; homosexual women often refer to themselves as gay, and the fact that the previous clause is correct English in itself should be self-evident as to my point. And yet, over and over again I see those two words being used alongside lesbian (like this article which uses the phrase “homosexuals and lesbians”), as if lesbians are some magical creatures apart from the rest of the gay world.
Men, being the default, don’t have a special word for them. But women often have such special status markers as lesbian and Mrs., not to mention that most of the time they are lumped into the markers that carry a male connotation such as gays and guys. Thought not as common, as the newspaper article linked in the first paragraph illustrates, this tendency to construe the male as neutral (and the neutral as male) bleeds into words that, as a clear part of their definition, are gender neutral.
Such male normative language bleeds into male normative thinking, which ends up reinforcing the idea of men as normal and women as Other. If lesbians can’t even be properly included in the term homosexual, then what hope is there for them to be seen as full participants in the queer community?