I don't think it's a post-2000s thing. In a year where hundreds graduated with a CS degree, I think there might have been around 15 females in my year (1994).

My brother did CS as well (mid-1980s). There might have been only one female in his year. There might have been more, but he never spoke about them that I can remember.

I suspect the gender bias has been around for a long time.