What's Wrong with Hair?
Unless you have a bald head, you will regularly go to the hairdresser to have your hair styled. You wash it, take care of it, and nobody will say that your hair is dirty. That is a bit different from body and pubic hair. Many people see that as 'unhygienic.'
Is Pubic Hair Unsanitary?
Some women (and men) like a nice patch of chest hair on a man. Others prefer to have no body hair. So many people, so many preferences. Although that does not apply to leg and armpit hair in women, as hairless is the trend there. As far as pubic hair is concerned, we generally prefer to see an (almost) bald cat and hairless male genitals. No more full forests of the past that were thought to be rather unsanitary!
If you take good care of your hair, head, body, and pubic hair, having hair is not unhygienic. Bald pubes are literally killing for the pubic lice, a parasite has almost died out since 'bald or shaved' has been the norm.
Aesthetically More Beautiful
Hygiene doesn't have much to do with it. A bald cat that is not washed is much dirtier than a freshly washed vagina with hair. Hair preferences are, therefore, primarily a matter of aesthetic. People see it as more beautiful or erotic when a woman or man is (almost) hairless. There are even people who think that sexual pleasure is more intense when the hair is removed. Hair removal seems, therefore, to only have advantages. It only seems that way, though, because hair removal often leads to inflammation of hair follicles. And if you happen to skip a day with hair removal, it can sometimes become a stinging — and certainly irritating — condition. Hair removal requires upkeep.