The Thai prostitutes come mainly from Isan in northeastern Thailand, not from Cambodia.
Though I like your premise about capitalism, Cambodia also is a fairly capitalist society, but with a lot of corruption and a kleptocratic government.
The real problem is that these rural societies which are dirt, dirt poor don't provide too many chances for education or training.
In another 5-10 years the Patpong district will go the way of the Combat Zone in Boston and Times Square in NYC. Going into one of those Thai bars and seeing the show to me was one of the most depressing sites I had ever witnessed. You could see that these people were totally exploited.