I mean I totally understand your frustration, but there’s an answer to that?
And the answer is that a lot of these kids are very isolated: they don’t have a robust, expansive adult queer community around them or accessible to them, for all the same reasons that teens have always not got to have that, ranging from one just not existing through to not being able to go to it due to parental prejudice or even just not being the kind of person who feels comfortable showing up to a new place.
So they find tumblr and tumblr is the first place that they find any non-straight “community” at all and then run straight into TERF-y bullshit but the people peddling that bullshit are telling them that This Is The Real History.
And they’re teens: no, they don’t necessarily know how to swim through the vast internet and actually evaluate the available sources, and the JSTOR articles often require an account and sometimes a paywall and are pretty inaccessible to your average teenager trying to figure out history anyway, and the books aren’t available (and you can find just as much TERFy bullshit in some of the books) and … so on.
It’s why this shit happens on tumblr: it gets very little traction in face-to-face spaces, and the big players - the adult women pulling this shit and pushing this shit - damn well know it, and know that if they show up to, say, Vancouver Pride with their exclusionist bullshit they’re going to get a bunch of fully adult angry LGBTQAI2S+* people in their faces, many of them able to go I WAS THERE DON’T TRY THAT SHIT ON HERE.
But if they can find the teens who don’t have a face-to-face community right here on tumblr and other online spaces? Well then. They get to have all the authority of having been The First Lesbian Adults/Voices those teens hear, of being the ones who set the tone and “establish” what lesbian history is, and voilà, you get sixteen-year-olds telling women who’ve been living as “butch” and “femme” for three, four, five decades that no!!!! those are LESBIAN ONLY TERMS!!!! et cetera.
And unfortunately, given that we’re still fighting to even let schools have fucking GSA/QSA spaces in so much of even the most “progressive” parts of the world, there are a lot of those isolated kids, and it’s not like they HAVE ever had the opportunity to learn anything else.
It’s a shitty situation. Unfortunately.
*(for anyone not familiar, the 2S is for two-spirit, who generally speaking have not just zero time for settler TERFy bs but, like. Significant NEGATIVE amounts of time for it)