I don't get it. Maybe it's because I like women, but I like seeing women out on the trails. I don't really interact with them except to ask them to pass, or make room for them to pass me (there's plenty of them that are way fitter than me). When I see them I typically wish my wife would join me on the trails, but alas, it's not her thing. I haven't witnessed what you've experienced, but it's likely that they do it when others aren't around to notice. I'll keep my eye out for it.