The expression "Sex sells" surely won't be new to you? The media reflects the interests of the society it serves; it has to, since otherwise no-one would pay for it. A more fundamental question, then, might be "Why is society obsessed with sex?" - but then that would be much more obvious, wouldn't it? Since we are all here to reproduce, and to send out greedy jealous genes on to their next generation, we're all interested in sex, body types and shapes, and how to sow the seeds of the next human beings in our lines. It's all very simple, no?