A perfect market would have people doing exactly what you are thinking of doing; buying cheap in the US and selling high in KR.
Eventually US price would be brought up and KR price brought down to an equillibrium.
I remember KR has a lot of laws about using some sort of social government ID number to register for social media... is that necessary for account on Korbit? This is a hurdle for foreigners to enter your market. Also, it is also difficult for Koreans to create accounts with exchanges overseas as well, so I think that is also difficult.
We have the same thing happening in Japan. Our price is higher.
It is because of difficulty of transferring money from KRW to USD and making accounts over seas.
This is very interesting. I saw Korea as a developed and quite free country. Reading the necessity of an ID for social media and dificulties of converting KRW to USD sounds really surprising. This would mean that it is so difficult to do arbitrage by sending money out of Korea, that the cost would equal 40-50%! In the case of Japan having a 20% higher price is understandable still... but 40-50% is really too much...