Some dogs just don’t like to take a bath.
I’ve read somewhere that this might be related to their hypersensitive smell ability: as we already know, scientists report that a dog’s sense of smell is 10,000 to 100,000 times more acute than a human’s. One of the reasons a dog has a much better smelling ability than we do has to do with the number of scent receptors: For every scent receptor a human has, a dog has about 50.
So our friends are used to their own smell, so when you bath them, you change the whole odor perception they have for themselves. It’s like a revolution. And they don’t like revolutions. (I guess nobody likes them). They just love their own smell that you simply dare to erase when you bath them.