I have photographed many people whose names can not be revealed, whose faces can not be shown, or whose photos can not be displayed. Why? Because they have a job; some are doctors, others engineers, others take care of children. Everyone has a job and everyone is afraid that a photograph of their body may cause them to lose their job or even destroy their career.
It's absurd, but it's real. People are afraid that the image of their body can end their future. And the worst thing is that they are possibly right. We live in a society, in which if others see our body, they can cause us serious problems (sometimes I wonder if it is true that the human being is the most intelligent of creation)
Then... why they posed naked? They posed nude because love to be nice-looking and to see that they have a beautiful body. Because the human body is beautiful, even if it is forbidden.