I think the reason for the general preference for female nudes can be traced back to a particular response to the classical tradition - one which has shaped western art since the Renaissance.
In classic Aristotelian biology, the male body is perfect, beautiful and good. Masculine nudity in classical Greece was virtually synonomous with civilisation itself: the body was clean, efficient, public - it expressed the virtues of a rational, assertive, warrior society.
The female body, by contrast, was innately defective, chaotic, soft, malformed: women were intuitive and emotional not rational.
Aristotelian thought shaped western consciousness but from the late middle ages one finds a new, essentially Platonic ethos developing: one which asserts the imaginative, private, intuitive and emotional. It manifests as what we might describe as the reinvention of art as personal expression. Given the cultural background, I would argue that the female body was the natural symbolic medium for the expression of this change, and remains so.
All the best, Ian