Thank you ThisFluentBiscuit for sticking with this discussion. I loved your 'snapping back elastic' comment - I think it's a really good way of explaining unconscious bias about all sorts of -isms.
There has been an effort to get more girls interested in STEM, and it has worked to an extent. But alongside this, there has been an un-official campaign against this in popular culture/social media etc. There's an undercurrent of 'brainy girls are yuk' 'boys don't fancy brainy girls' 'brainy girls can't do make-up right' 'brainy girls are lezzies'.
Although we are sometimes accused of being obsessed with transgender issues and dragging trans into everything, there IS a link here because the trans movement has pushed a version of femininity that is exaggeratedly 'girly' - the make-up, the giggling, the head-tilt, the voice, the walk, the airheadedness.
That out of date version of 'how to be female' which feminists hoped had been consigned to the dustbin of history [and then burnt
] has now been resurrected and mainstreamed.
The trans version of woman-ing is feeding back to girls - if you want to be a 'real' girly girl, the best-known examples of 'real' femininity are as likely to be trans males/drag queens as real females.
And if 'being a girl' means being as fluffy and twirly and giggly as a transwoman, a girl who doesn't want to be fluffy and twirly and giggly must be a ...boy.
Cue the dangers of transition, puberty blockers, surgery.