Keypunch operators were overwhelmingly women, but skilled programming was never substantially female. The obsolescence of "secretarial programming" (ie., retyping, keypunching, etc.) is the principle cause of the gender shift. Gender ratio in "formal programming" has always been ~4:1 M:F, including today.

Given now ~two decades of affirmative action for women getting into technology, and many high-status "professional industries" now dominated by women, the idea that the best explanation of this ratio is 70s/80s culture is implausible.

What we have seen, instead, is that as women are more free to choose professions the percentage of women's involvement drops.