Mistress Suki felt that her slave was thick and that was not a good thing for her. She felt that it was important for the guy to learn his lesson and for him to try and educate himself than her trying to always deal with his thick head. So she trampled his head painfully to make him get that. He got it because of the pain and he tried his best to change.
Mistress Dula and her friends lined up their boyfriends and they trampled them because they had dad bods. The mistresses did not find those funny or interesting and so they had to make them as a collective to start working out the same way they did. The mistresses were all in shape and they wanted their men to also be. They had no choice after the domination they were subjected to.