Language barriers, timezones (their night is our day; it is flipped). Most skilled Korean software engineers end up in the Valley. Remote development only goes so far.
The timezone is similar: India is 10 hours forward from America/New_York, RoK is 12 hours forward. Flights to RoK (12-14 hours) are actually significantly shorter than flights to India (20 hours).
Indians are probably paid less than Koreans, but I don't know. And I cannot speak to the technical proficiencies of either.
I'd definitely like to open an office in RoK some time.
If anyone on here has done so or is interested, send me an email.