I was interested in high school but felt like I wasn't allowed in the computer room. It was full of boys who knew the teacher, and I didn't know the teacher and wasn't a boy, and just didn't really want to deal with the social discomfort given that I had a computer at home and could use that for an hour in the evening. Instead I skipped class in a computer-less room with the IB coordinator's blessing.

That hour or two a day of skipping class or eating lunch would have had a different effect if I'd spent all the time playing with computers.

I started making up for it in college as a CS class was required, I couldn't afford my own computer & so discovered the trash and Linux, and there was a badass female sysadmin who demonstrated perfect ease in owning the computer lab.

Which came first, tool-toy companies interested in boys, or boys interested in them?

Maybe it doesn't matter. Once a group becomes predominantly one culture, it rapidly slides to that corner of the culture space. Lots of reasons - people hire people they feel comfortable with. People value people they understand more, regarding them as more intelligent or harder working.

You say "ever" but the early history of computing was filled with women. Something caused a change.

The field was too small at the time to draw any useful conclusions.