I have a theory about why this changed in the 1980's in particular.
- The 1980's saw the dawn of personal computers, and many people either bought them or brought them home from work.
- Personal computers, especially the inner workings and programmability appeal very much to people with Asperger's and high-functioning autism, as they present a highly complex but perfectly logical and predictable user interface. Because of this appeal, a much higher proportion of young people on the Autism spectrum learned to program computers (that their parents had at home) long before they went to college.
- Autism and Asperger's occur more frequently among boys than girls.
- Because so many "geeky" (i.e. autism spectrum) kids, mostly boys, got into computers during their high school years. This in turn likely caused neurotypical people (of whom more are girls than boys - remember autism occurs more frequently in boys) to associate computers with "geekiness" and caused them to gravitate towards less "geeky" hobbies and interests.
The key, I think, to making computers more appealing to girls is to dis-associate computers with social "uncoolness", and a lot has been done towards this end in the last 10 years.
EDIT: I'm getting some downvotes and I'm curious - do people disagree with or not like my theory about the connection between male representation in software and autism? I really don't think it's sexist to observe that autism occurs more frequently in men...