Is it just a nude?

What makes a nude presentable? I suppose there are a lot of answers to such an open ended question. But I have noticed first hand over the years one particular factor that definitely affects the ability to sell a piece. That is when I looked at the number of gallery sales of my work; I realized that more people buy nudes where the model is not identifiable. An anonymous figure might make it to the living room wall. A beautiful woman...seems to be harder to justify in the eyes of the discerning public.
Something happens when a nude becomes a complete woman. I guess it then becomes a portrait.... and a nude. In some way it loses its sense of abstraction with the loss of its anonymity. I don't think this idea makes it any less beautiful. In fact, it creates opportunity for more layers of expression, (subtle or obvious). It seems odd that humanizing a nude by making it an identifiable individual would create....I'm not sure what it is... a level of discomfort? Why?
Maybe its because people feel they need to know the person to justify owning and displaying the piece. Does that mean that the piece is something more (or different) than a work of Art? Maybe. Or is it a semi conscious social taboo that stirs up some level of uncomfortability with having a naked woman in the room?... a stranger at that.