If it weren't for the stigma, this wouldn't pay so well.
The money we get is partly risk pay and partly pay for being willing to sacrifice a lot of other things in order to be available for hire.
You are making a good point here Fabulassie, however, I work in Switzerland and rates here seem higher than in London (but maybe it's just my experience because London doesn't really work for me when I am touring 3-4 days, I only get regulars that I met in Switzerland) although it is legal and you get a lot of support here.
The social stigma is of course still there but I don't think it really makes a difference in what people are ready to pay for it.
Sex is sex and men will always be in need of it, and the more sophisticated ones will always want more than a simple street walker (I apologize if that sounds judgmental) and ready to pay for the difference in service and quality.