If cuddling, curiosity, kissing, genital stimulation, pubertal stress and unrestricted sexual license are not enough to compel people to mate, there is the added, overwhelming influence of peers who are experiencing the same thing. Since none of them can join the orgy unless they have someone to party with, there are hordes of humans devoting an inordinate amount of time to seducing each other in a world where people, especially young people, dread being ostracized from society by their peers.
Boys, being larger and more muscular, sometimes rely on force if nothing else works. Girls, being unable in most cases to forcefully compel a boy to carry out their fantasies, learn how to dress and how to pose and what to say so that boys will be much more likely to do as is desired. In some extreme cases, girls have humiliated boys into sexual activities by questioning their manhood.
The young become so intent on using each others' bodies for various forms of distraction, ranging from cuddly romance to dominance and submission, that various societies have developed beliefs that there is something wrong with anyone who does not mate at will. This stereotype exerts even more pressure on people to mate indiscriminately, especially on inexperienced, pubertal youth who do not understand that social conventions can be and have often been resoundingly counterproductive or, more to the point, massively destructive.