What is it with the fascination with butts and anal sex kink?

The shape of a woman's butt is nice yeah, but anal sex, or even playing with someone's ass hole during sex is like 'what were they thinking'? Do women in general really like their butthole played with during sex?

What is the erotic fascination women (maybe some men too?) have around buttplugs?

Never been in a situation where I could ask women in person.