But the tech industry is also famously self-selective. Many people in the industry self-selected for it when they were pre-teens. Spending hours upon hours programming in BASIC or whatever on their C64s or TRS-80s before they were out of elementary school...before thoughts of sexism enter the consciousness. There is very little preventing young girls from getting involved with tech at a very young age except simple lack of interest.
Anecdotally, I remember growing up and horsing around with many friends on our 8-bit computers before any of us had 2-digit ages. As I grew up the friends and computers changed, but the basic demographic didn't. When my peer group hit puberty we would have killed a member of the peer group to get a girl involved in our group of nerds.
Many of my friends had sisters, none of their sisters cared the first thing about what we were doing. A few of their sisters showed some interest at times, but always seemed to have other priorities. This must be a shared experience as the type of group arrangement in the Big Bang Theory resonates with all of the tech industry males I know.
It wasn't until half-way through high-school that we finally lured a couple of girls into our group, but we spent most of the time teaching them basic computer skills than nerding out with them. Nevertheless I never heard anybody put the female members of our group down, or act like they weren't capable of eventually doing the high-nerd things that we were doing. To the person, everybody was helpful, and the girls hung around and one even tried her hand at majoring in CS...before changing majors to International Relations.
Happily, things have changed for the better. The number of women in tech has dramatically increased since those early days. It's not 50/50 by any stretch of the imagination. But there are actual women in tech these days doing cool things. They've self-selected to enter it and have put in the time to become good at it, and have managed to ignore the real sexism (such as it is) and that's very very cool.
It's an additional barrier that many males don't have to deal with, but I think self-selection at an early age is an even larger one.