Why dose everyone always talk about sex?

I just dont get it. Its on everybodys lips. Yesterday i was walking around downtown and herd this group of girls talking about all the guys they had sex with recently and what they did. I think its grose. What happend when sex wasnt talked about in public and people hid hickys insted of flaunting them? It seems like sex is used as a statis thing? Anyways please someone explaine this all to me. I still feel blushful when a song comes on the radio thats sexual.