Princess Serena has an ass to die for and she knows it. She does not believe that her ass is just for sitting and being spanked or fucked. She wanted to make money from it and that is why it is a prominent feature of her findom fetish. She enjoys teasing guys with it and then dominating them financially. The guys cannot resist it and her and she knows it.
Mistress Jenny had a massive project to carry out. She wanted a good amount of money to carry it out and she did it using the money she got from this loser. She financially dominated him and she made sure she got all she could from him. She then went to a different loser and she got more money from him. She combined all the money she had gotten from all the slaves and that is how she financially dominated them and financed her project.