Programming is a solitary activity where you solve logic puzzles. Anyone can do it. Another activity that is very similar is playing chess - yet no one is up in arms that chess schools aren't including 50% girls in elite chess training.

If you took a group of girls and a group of boys and put them in a room where they played chess for a few hours, then asked them how much they enjoyed it... more boys would rate the activity higher. Is it because some stupid poster on the wall??? No it's not. On average, men and women are different and have different average preferences.

Programming is not an activity where you need social support groups to succeed. It's the one activity where being a hermit who takes initiative and learns everything themselves can be an advantage over being more social. A large portion of programmers are self-taught online, and just start tinkering with things because they enjoy the activity. You can't force that.