Who isn't? I suppose it is a gift that we humans have. Animals don't have sex... they fertilize one another and they reproduce. And they do so when the time comes for them to do so. We human beings don't simply fertilize or reproduce. Otherwise, sex would be just a slam-bang-thank-you-ma'am affair. Oh no. Sex is something we get curious about, we try to get some experience of it, we savor the experience and we try to get some more, whether it is time for us to do so or not. That is also why human beings suffer from sexual dysfunctions and animals -- strictly speaking -- don't.
The Jewish Bible presents sex as a gift that God included in his package for Adam. It is narrated that He himself leads the woman Eve to the slumbering Adam. Read it in Genesis 2. Man, the dialogues in the story is terse ( I suppose it is a characteristic of all stories in the Bible). When Adam sees Eve for the first time, he says: "At last, here is bone of my bone and flesh of my flesh. You shall be called Woman". The remark may be short, but it says a lot about what all males in Adam SHOULD want to see in a female: a companion. Later, when Adam had eaten of the fruit of the tree of knowledge of good and evil, he would notice Eve's nakedness. And from that moment on, it is the only thing all men seem to want about women.
"Sex" -- philosophers tell us -- is what makes a man different from a woman and vice versa. Later, "sex" became identified with the genitals of the male and female, since these distinguish them physically from one another. The so-called "sex act" is of course what a man and a woman does with their genitals. And later still, people no longer talked about the "sex act" since it was easier to say "sex" in a sentence like "'Let's have sex" rather than to say something awkward like "Let's do the sex act." So "sex" finally came to mean the "sexual act". And, during these times of sexual confusion, it can refer to the genital activities between a man and another man and a woman with another woman (with the prefix "homo" prefixed to it, of course. Although I doubt it whether gays and lesbians would say "Let's have homosex" or something like that.)
The term "fuck" is also used in place of "sex". It is a word that earlier served as an acronym for a crime. F.U.C.K. stood for "For Unlawful Carnal Knowledge" and it was acronym that was hung on the neck of a criminal to inform others about the reasons for his/her arrest. Unlawful Carnal Knowledge covered "rape", "adultery" and other "carnal" acts that are unacceptable.
Some purists say that there is so much of sex around that it has become cheap. Well, when we talk of the Law of Supply and Demand, that would indeed the case: the more the supply the lower the price. But where do we find sex? Billboard advertisements, moviehouses (both onscreen with audience participation at times), tabloids and comic books, computer games, radio programs, the internet... You name it, it is there (or will be there).