There is a classic saying, I think it traces back to Shakespeare or maybe even Chaucer, but anyways, the saying goes “once you go butt, you never go back.”
Since the dawn of time, people have always wanted to put their d*ck somewhere warm and tight. Whether that be a warm apple pie or a butt hole, it’s just human nature.
Although the vagina is where the holier than thou clitoris is located, heterosexual couples can’t help traveling to the back every once in a while. And why the hell not? The view is fine, and the humping is divine!