It's not that they're exploited. Cambodia's economy is just really, really inefficient. Food prices in Cambodia are really high (ep 4), higher even than in Berlin [0] by 21%, not to mention Eastern Europe (2+ times Warsaw's prices, 4x if you shop around).
The sad thing is, the wages in sweatshops won't go up much. Sooner or later automation will advance to the point where even $3/day for sewing garments will be too high and they will all be fired.
[0] http://www.numbeo.com/cost-of-living/compare_cities.jsp?coun...