What is the psychology that causes me to have fantasies? Why can't I be by consensual ?

Some things I have read is that maybe people who want to be in that position of control were (in the past) abused, humiliated or put in situations of helplessness and they want to project it onto someone else. Like, have someone else know what it feels like. Im not saying that your fantasies have to be a direct result of cirstances like that, but it is common. Maybe if you were to get a partner that enjoys the same fantasies your desire for it wouldn't grow to an unsafe state. It can be categorized as 'predatory behavior'. Talking about it to someone would best help you figure out your situation because everyone is different.