Well, I would assume if a hooker got busted, then set free, they would have that on their criminal record. So when they apply for a job, they have to mention that, and it wouldn't be too surprsising if many employers wouldn't want to hire someone with a felony on their record. As a result, they seem to go back to doing the only thing that they can do. It's the same case with a lot of criminals, and why they go back to jail shortly after getting out.
The real question I think we should be asking is why hookering is illegal to begin with.