The concept of sexual orientation has only been around for 200 years. The decision that sexual orientation should be based on one’s gender is arbitrary and vestigial. This becomes obvious when we consider the existence of nonbinary people.

Is an enby exclusively attracted to women a lesbian? Did your brain reflexively attempt to consider what that enby’s Assigned Gender At Birth was? That’d be bad. The proper conclusion here is that anyone who identifies as a lesbian is a lesbian, including transmasc people.

The synthesis here being: Sexual Orientation has nothing to do with one’s own gender.