* Girls are often put under more social obligations than boys. Look around and you'll find lots of stories where girls are expected to help out with the housework while their brothers are given free reign to do what they feel like.

* I deeply believe that representation matters. Many girls probably never even considered that computers were a thing they might enjoy because they never saw other girls being into it.

* This less true today, but there has historically been a lot of pressure on girls and boys to do gendered activities, and tech was male coded. Parents would tell their daughters to play with dolls, not videogames. (And videogames are very often the pathway into programming.) Peers would make fun of girls that were interested in nerd stuff.

* For reasons that aren't entirely clear to me, male nerd culture has often been outright hostile to females entering the space. Girls trying to join programming clubs, take CS classes, etc. would frequently get harassed by guys. (You can look at Gamergate as an extreme example of this.)

Meanwhile, male found it easy to think of being into computers because almost everyone you saw using a computer was a male like them. They were given ample free time, and faced few headwinds when expressing an interest in tech.