I’d be sexist if I said it was women’s nature and blah whatever. I’m sure it’s more or less a social matter, nevermind that as far as I know it applies to pretty much any known culture, ancient or actual. The reason might be that humans are not so different actually, no matter what your fucking leaders might tell you. And you, Mr “pickup artist” might notice that I did not refer to the sort of occasion you’re talking about. The situation the OP describes is obviously not an invitation to a menage a trois.