Can you think of a less erotic place than a kitchen? Why do so many ladies pose in a kitchen in front of the table or sink or stove or washing machine or some other gadget in - or out of - their lingerie, and imagine it is a turn on for the punters?
I shall not even bother to post a link, there are too many.
Afterthought:clicked on modify: actually on the bog is often even less erotic unless that happens to be your thing. Some ladies are even photographed sitting on the bog of all places.
The back of an old mini would be less erotic. With regards on the bog shots, these may appeal to WS and scat fetishists, but also voyeurs as it is an invasion of personal space. To some people seeing a woman piss is taboo, so it becomes desirable.
Kitchens are usually clean places, sometimes the best designed room in the house, once again it has technology (cooker, microwave, dishwasher etc) so you've got a clean space, a hot woman and some technology, sounds good to me.
But, it's worth noting kitchens are sometimes the brightest room in a house, hence it's easier to take photos in.