lovedoctor anon here..
It's actually hygienic, like shaving one's head. some cultures do it, some don't.. a lot of cultures don't even kiss actually.. thats kind of a european oral fixation thing.
personally I believe every type of hygiene comes with pros and cons.. overall having long hair, a beard and a bush is superior, but only when given bit more care. a tasteful amount of kissing is good.. but there's little reason for excess.