Well it's obviously because before widespread reliable contraception, the welfare state and non-physical office jobs, sleeping around was a great recipe for getting knocked up and then not being able to provide for your children. Therefore women who slept around were vilified by communities because they knew they'd be the ones who had to take on the burden.
The emergence of the above things has only happened since WW2 or 1 if you want to be generous. That means there are only a couple of generations who grew up without it being a concern, and even they will have been influenced by the still surviving grandparents, parents etc. Even so, second-wave feminism (social and family issues) began pretty quickly after the socioeconomic changes and was a strong movement with the tide of history behind it.
Nevertheless, just as there are a lot of people who think in terms of family and community support despite the welfare state, there are a lot of people who still retain the tacit assumption that women shouldn't sleep around.
I am all for women sleeping around, being sexually provocative and so on. It's sexy. Although as a believer in hypergamy I'm not sure they're biologically wired to spread the sex around the pool of males.