It's that the profession acquired status and $$. Mid-90s into the .com boom transformed it from a nerdy but niche profession/obsession into one with status.
Anytime that happens, the gatekeepers start to dominate.
That's my guess, anyways. I got into this work for pay in the mid-90s, not earlier, so I'll take your word for it that there was a time when women were more prominent.