Turkish, like many airlines in the developing world, enjoys a substantial labor cost advantage to Delta. Turkish hasn't released its 2011 full-year results yet, but in 2010 its personnel costs were just 60% of its fuel costs. At Delta, labor costs were 89% of its fuel costs in 2010. Same reason that EK has a huge advantage over every USA-based airline - low labor costs. Turkish has a good reputation for quality and safety and thus, not surprising that its frequencies to the USA have increased over the years without much competition from USA-based airlines.