I don't know why, but this is so sexy!
Males are hard-wired to be aroused by this female position. It was the primary mating position for many centuries as we evolved... There was no etiquette concerning sex; men would take women in any venue or while they were busy doing other things. It wasn't unheard of for multiple rapes moments after a woman gave birth. Until we stopped our nomadic ways and started cultivating, and creating villages humans were a fairly straight forward group of despots...