Lady Stefanie was of the opinion that this guy needed to learn his lesson and that the best way for her to do it to him was for her to trample him and also smother him with her ass. She had him worship her ass after she was done doing what she wanted to him and he was not in a position to say no to her as he knew what would happen.
Lady Stefanie wanted this slave to worship her ass and he did it as he had no alternative. He knew that when she had decided on something, there was no convincing her otherwise. That is why he did it the way she wanted so that it would be over quickly. The mistress liked what the slave did and how he did it that she rewarded him when he was done.