I think there's room for more nuance between losing a limb because you're so sure no gay man would have a problem with sleeping with somebody who has a vulva, and calling gay men who do so, bisexual.
Lesbians and gay men holding their breath and sleeping with somebody of the opposite sex isn't new. Sometimes it's about not coming to terms with your sexuality yet, and sometimes (particularly historically) it's unsafe to be openly homosexual so you do what society expects of you to try to fit in. I don't think those people are any less homosexual than those who have been able to be clear and open and only sleep with same sex from the word go. Life is more messy and nuanced than that.
I think one of the modern challenges is that a lot of people want to #BeKind, and that includes homosexual people. I imagine a higher % of LGB people are politically Left wing, and there is a lot of pressure from, well, everywhere but the political Left for sure, to accept TWAW and TMAM. I'm fairly sure those who include trans identifying people may be doingvmental gymnastics to override their natural ick about it, and I don't think it necessarily makes them bi.
Of course I do think there will be a much higher % of lesbians who are trying to #BeKind and incur trans identifying people than of gay men, because women are raised to be kind, accommodate, put others first way more than men are.