Mistress Madison and her friend needed to do some stuff for their own pleasure. That is why they had to dominate and humiliate him for what he had done. The poor guy found himself being used as a human toilet and he had to drink their pee. He was turned into a source of pleasure for them and there was nothing he could do about it. He had to comply.
Mistress Madison was tired of trying to pass a message to this guy and him not understanding her. She was fed up and she had to do something about it. That is why she chose to use her piss femdom to dominate him. He had to get the message one way or another and she did this using her pee. As he drank her pee, he realized he had to learn to get what she said to him.