I’d wager it’s the same as the composition of females in any Engineering program. If there were 25 women in your CS program out of a 100 (being generous), they can’t magically multiply and somehow end up 50 in the workforce.
No one is forcing them to NOT join a STEM field. Everyone is telling them to specifically join STEM and giving likely billions of dollars in support aiding the increase.
As someone who's raised funds for a program for HS girls in STEM recently, it seems like those 'billions of dollars' are all going to advertising or something 'cause they're sure not coming to, say, pay for teachers for my artificial intelligence camp.
No one is forcing them to NOT join a STEM field. Everyone is telling them to specifically join STEM and giving likely billions of dollars in support aiding the increase.