Because no man wants to think about the man! And porn is marketed to men. There's a reason he's called the "stunt cock." Quite a few men get off on the idea of HER wanting it. SHE wants the huge cock, she is insatiable. The idea is that the woman/women is a sexual beast who wants you so badly ... which is what the man behind his computer/TV wants because most porn watchers are not indulging with another viewer. The man always must orgasm, but no male viewer wants to see him any more than possible. See also, POV porn.