Today we face a similar taboo, held for similar quasi-religious reasons. Our latest epicycle is competitive job postings. This at least is laudably specific; most of these kinds of explanations aren't testable at all.
The obvious but taboo answer is that women will generally gravitate to fields which are more social/people focused and less technical/mathematical. That spectrum runs from teaching through medicine in the middle through CS.
These trends are due in nontrivial part to genetics. Women are just more social and men more systematizing, on average.
As programming went from rote punch card/data entry to something more like physics or math, the percentage of women dropped.
All this breast beating is about a refusal to accept that basic biological differences could possibly affect behavior. Indeed, not even the tenured President of Harvard can broach the topic, even if he only moots the possibility of differences in variance rather than mean!
It's not much of a debate when those who voice the "partially genetic" position are at risk of losing their jobs.