Word swap

There's an interesting article in the Guardian about the translation of Han Kang's award-winning Korean novel The Vegetarian. It's been difficult for English-reading critics to assess the novel, as the translation seems to feature both basic errors and tonal changes. I'm interested to know why finding a truly gifted Korean-to-English translator seems to be so difficult. I've been hearing about people working in South Korea as English tutors for years; surely some of them became truly fluent in Korean while they were there?