People do it for the buzz of will they or wont they, seeing a new face amongst the usual hookers when they drive past is enough to make some folk risk it, and at a low price they just think well its only a tenner!, and don't think about what the price will be if they are caught by police, mugged, or get infected.
There are many parlours who would take girls from the street, but because they don't want to work 9-10 hour shifts, or are not able to get their act together on a regular basis, so if you put these girls all together in a RLD, don't you think the pimps are just going to control the area still.