The female bathhouse employees all have humanoid appearances, while the male workers, besides Haku and Kamaji, are all frogs. Why do none of the workers, besides Kamaji (always in his "spider" form) and Haku (in his dragon form), ever transform into their actual spirit forms? Lin/Rin is a weasel spirit, but she never transforms into something like a weasel, and the yuna are spirits of slugs, but they never transform either. Not that they would want to transform into a weasel or slug, but do they even still have the ability to, like Haku into a dragon?
And what about the customers? Although they don't either, can they transform into humanoid appearances?