Goddess Nastya needed to shit on this guy and she did it because the guy was wild and she did not want to continue with that nonsense. The mistress felt that the best thing to do to him was to use her shit fetish to humiliate him and she did it after she had used her big tits to tease him. He took the bait and she had fun at his expense.
Goddess Nastya found this guy to be unreliable and she had to do whatever was in her power to dominate and torture him. That is why she did what she did. It was cruel and humiliating for him but he had no choice but to do it. The mistress tied him up and she went ahead to make him a human toilet and he had to eat her poop and drink pee.
Goddess Nastya likes to get her way and she felt that if she used her shit on this guy, she would easily get her way. So she did not bother thinking twice about it and she went ahead to dominate as well as degrade him. He cried but by the end of it, he had no option but to eat the poo. She then let him clean up after himself.