I think I need to point something out here.
The current US population is a little over 307,000,000 people. The current population of the Czech Republic, Armenia, Bulgaria and Iceland(countries that have a, for lack of a better word, robust sex trade) is 10,000,000, 3,230,100, 7,500,000 and 319,000 respectively.
5,000 in CZ's 10,000,000 is about .0005%, 10,000 in the US's 307,000,000 is about .000003257%. I point this out to show a scale of number of sex slaves per capita, if that makes any sense. Basically, even though there are more instances, it happens less often.
Moreover, the estimated number of people trafficked in countries is about 600,000-800,000 globally each year. At 10,000 each year, the US sex trade makes up about .167-.125% of the annual global trade. I attribute this in part to our rather forceful approach to the sex trade(we even have a "czar" for it, established under Bush the Younger).
My point is, the sex trade in the US does indeed exist, but we are combating it and are taking a far more proactive approach than other countries. It is more prudent to start putting pressure on countries like the ones mentioned above where they aren't.
To be completely fair, Canada, Britain, most of Western Europe, Austrailia, New Zealand, Morocco, French Guyana, and Colombia are up-ing their methods too.
To give you a better idea, here's a map illustrating it. Yellow areas are doing "something," red areas are doing nothing, green areas are up to the US code, and the gray areas have no data.
http://en.wikipedia.org/wiki/File:Trafficking_in_Persons_Report_2005.png