The trouble is that being an expat at Korean and being an expat at EK are two totally different jobs but I suspect some think that since they have adapted to the cultural melting pot that is EK, then they will easily adapt to Korean. This is sadly never going to be the case for all.
Having been an ex-pat at other companies prior to EK and where I was the minority in amongst a single majority based on nationality, I can see how some will simply just not be able to adapt to working at Korean, with all the nuances that go hand in hand with working there.