Your question has a bit of a misconception (for chess at least) - there aren't "men's" and "women's" sections, there are "open" (everyone, including men and women) and "women's" (women only). In other words, women are free to join pretty much any event for which they are qualified. I don't have the historical knowledge as to how this came about, but there have been a bunch of threads in recent days about this in /r/chess, so you may want to check there for what the current justifications are.