People have sex for a wide variety of reasons. Whether it's penetrative sex, oral sex, or masturbation, sexual activity is an integral part of human biology that can be a source of pleasure for many people.
The most obvious reason people have sex is for procreation. However, people usually start having sex long before they want to have children and continue after they do. Moreover, birth control has made it possible for people to have sex without the risk of pregnancy.
In the United States, the average marriage age is thirty-three and people in their late teens and twenties tend to have more sex than older people. Nevertheless, there are many people who experience difficulty with penetration due to pelvic floor issues (like endometriosis or vulvodynia) or erectile problems. They may still want to experience intimacy and satisfaction in their relationships, but struggle with how to do so safely.
To address this issue, researchers asked men and women to list their reasons for having sex in two studies. Participants ranged in age from 17 to 52 years. They provided 237 reasons for engaging in sex, and factor analyses yielded four large factors and 13 subfactors that grouped together into a hierarchical taxonomy of motives: Stress Reduction, Pleasure, Physical Desirability, and Relationship-Building. Each of these motives can be boiled down to an emotional need that is fulfilled through sex. For example, some people who have vaginas find it easiest to get pleasure by using their hands for manual stimulation instead of a penis, so they are more likely to choose non-penetrative sex.