I assure you, medieval people bathed (2019)
Tangential question: Why do humans place emphasis on bathing, when most other animals don't seem to need to do it? (I think in the US we bathe more than we actually need to, but on the other hand I assume that the strong cross-cultural emphasis indicates that we do actually need to do it to some degree to stay healthy.) Maybe something about our unusual skin, and how we sweat to stay cool?