Mistress Tress was having fun at the expense of this guy and she did it because she felt like it and she wanted him to be humiliated like he had never been humiliated before. She facesat him and as he struggled to lick her ass and was choking, she took out her phone and she took a selfie. Never mind that she was already recording it on her video camera.
Mistress Annabelle wanted to shut her slave because he was talking too much while she wanted to enjoy her book in peace. When she gave him subtle clues that she did not want to be bothered but he did not get them, she had to use another method to get to him. So she settled on facesitting him because he would feel pain, he would choke a little but more importantly, he would shut up.