There is some ambiguity as to the reasons why artists drew from the female nude. It is my belief that it served a dual purpose. The academic gave it a kind of respectable veneer, while underneath it was a way for artists to satisfy their private desires.
Both the visual arts and pornography have centered on the male gaze. This is what makes them serve a similar function to the one viewing it. The subject is fully unaware that someone is looking at her. She is in another place and time from the viewer.