@PKMNB0YI think the amount of reverence for the rear end is probably being played up for comedy in the OOC to be honest.
Its probably more similar to like...
The Virgin Mary was considered to be apple breasted by a frack ton of Romance writters/painters during the Enlightenment Period. Because this was considered the quality of a sacred woman, it became a standard of beauty.
there are probably better examples, but the apple breasted thing was the first i could think of. Basically just 'known' (more likely assumed) properties of physical appearance steering social norms of what is le sexy.
edit: And that reinforcing itself and becoming more exaggerated (seriously, look through romance novels of that era. Every god damn woman is apple breasted. There had to be a fucking apple famine for generations these guys were so obsessed with apples.)
Edit 2: Or are we talking about the monster girl show? Cause no yeah thats straight up soft core. I mean, I liked the show (in part because I find the awkward way harem shows handle that kind of thing aboslutely hilarious).