I looked into this back in 2017 and figured out why there is a massive premium. It’s due to capital controls. I forgot which way but you could send your Bitcoin and sell it for their currency but you wouldn’t be able to get your usd back pretty much.
There is also the issue that you need to be a citizen just to open a bank account there. You can’t just open it online and wire money back and forth, won’t work.
If it was easy:.. there wouldn’t be a premium.
Spot on, depositing and selling the Bitcoins or other coin is very easy, but getting the money back in form of fiat is where the hurdle is. Ideally, getting someone whom you know from South Korea would work as they would help you sell and then send you back the money to buy more coins, but the problem is trust issues and sometimes other factors such as weird exchange rates by international transfer banks that can just eat up all the projected profits in a flash.
The situation is similar to that of exchanges like Yobit and hitbtc that keep wallets of certain coins under maintenance for ages.