In my opinion, it's science.
Brain chemicals and hormone production are likely the root of it, then layers of environment, upbringing, societal expectations, age, and open mindedness.

Hi. One of the first things my fiancee and I talked about after we met on match was Dom sub. This was not something either of us had put on our description so it was a pleasant surprise. I'd never been with anyone interested in it and resigned myself to just fantasies.