If we ask for the cause of something, we assume that it is about a disorder. In this question it's more so that we wonder why people do what they do. People tend to apply a certain norm in judging others and themselves. What we don't understand or find strange, we often reject. There are many theories that try to explain the origin of an aberrant sexual fantasy, thought or behavior in persons, but a final explanation is not known yet. We often assume that they originate or are formed in puberty. There are two important explanations for the development of sexual variation. Explanations that come from the idea of social development - how people treat each other - assume that something is wrong with the ability of these people to get involved in a relationship. This inability would be expressed in the form of sexual variation. Exhibitionism and voyeurism are then seen as clumsy attempts to make contact. Another explanation is that of coincidental connections between arousal and a certain situation or act. It is assumed that you want to repeat the experience that led to arousal.
Some behaviour, such as sadomachosism, is known to be related to having been submitted to violent abuse. Associating violence with sex has been a learned technique for surviving violent abuse.