This has been a "culture" on the internet for as long as I can remember, dating back to the first printed picture from a computer (or first sent image over internet?) being of a group woman and one of the standard test image (for early machine learning maybe?) was a woman in a suggestive pose (from Playboy or similar magazine if I remember correctly). The term "No one is a woman on the internet" has also been uttered for as long as I remember, although many of the early pioneers of computers were women and the space wouldn't have been the same without them.
There are women-only spaces on Reddit (or at least they claim to be, impossible to verify obviously) just like there are male-only spaces on Reddit (and both goes for the internet in general), you just need to know where to look.
> Any attempt by women to start a subreddit exclusively for women inevitably gets banned.
I would love to see where this has happened, as I haven't seen it before. I don't find it hard to believe, but want to see it happening in practice before jumping to any conclusions.
Edit: To add another example from this very submission, which is a common way of framing things (on the internet):
> Alright boys, I think I have figured out where the timeline went wrong [...]