Believe it or not, these girls must CHOOSE to display themselves in windows – if I am not mistaken, pimping is illegal. The girls pay monthly rent for these rooms/windows, which are apparently in high demand.
The rest – what Dom said. They are well-protected in Europe, especially Holland.
It is kind of a novelty for most people, even just to look – but since I live in Thailand, the windows in Holland are actually boring LOL. In Thailand they all sit behind one big glass window in a showcase.