Why does the derriere hold such avid appeal? Why do we compare it to peaches, bubbles, and bookshelves? Why do some of us wish to worship it in less than hygienic ways? If you're a lover of ass, the why doesn't matter.
"Don't quit your day job" is a catch-all when it comes to BDSM, not because a nice girl can't have the chops or beat down a 250-pound man. Most folks getting into kink want passion, excitement, and a break from boring. It's quite the mindf**k when a sweet-looking girl turns out to be methodically dirty, sadistic, and cruel.
The desire to be humiliated is pretty common. A boy or young man may think he is the only one who feels this way. It is a natural response to develop a humiliation fantasy as a coping mechanism. Bigger is better? Nope. Sometimes bigger is just bigger.