I think the main reason some clients are attracted to sites like this is the fact that is usually cheaper and they have plenty of time to go online and search.
If they're with a guy in exchange for money does it really matter how you meet them? I know escorts who have ads on SA just to search for a sugar daddy who might take them out of the business. I wonder if a certain Belgian met his Prince this way?
On the other side SA is bringing more young men to the business, and is a useful way to "test the waters", they can also screen potential clients and avoid those who they dislike the most.