The field of software business changed rapidly in the 80s. It shifted from a fairly boring and low-paying thing, into an unpleasant and high-pressure field where fortunes were made, even for regular employees (the stock options lottery). Salaries also went way up. It was only natural that men became much more interested in it at that point, and women's interest waned (they're far less inclined to kill themselves in a pointless job to get that $500k salary).
