Thank you for the question and your interest @ropaga. Nothing is too private. I am willung to discuss anything here and help increase awareness and understanding of the BDSM lifestyle.
What do I think it is the cause of dom/sub sex-fantasies? If you are asking as it relates to this post then I think it is a need for the Alpha male to find another of equal power or more powerful to test his level pf control. Quite often the fantasies of successful men involve being overpowered and put in helpless situations.
I feel this gives them a sense of great accomplishment afterwards and a deeper self awareness.
If you are asking a more general question about the overall motivations of the Dominant then read My next post... 😈