Why didnt Molag Bal show up in the DLC? We are dealing heavily with vampires, so i dont understand why he didnt even talk or make an effect

Because he doesn't waste time with lowlikes of man and mer, even if they worship him.

he is the daedric lord of domination (of humans and mer) he should be interested. thats like a car dealer being interested in customers. also he actively creates vampire lords and raqes women