Bithumb connects directly to your bank account, making it much easier to fund, which increases the supply of fiat relative to crypto. Also it is limited to Korean nationals by regulations, so any incoming crypto must come from other Koreans. Since few Koreans have any crypto, the supply is low.
I have opened a bank account in Korea in order to arb this, but I will still need a trusted local Korean national to comply with the new regulations, so I have not yet begun. There was one full arb cycle performed a few days ago, using bittrex and bithumb, but the spread is back. The new regulations broke that loop, presumptively.
I presume that Yoonsuh88 is a drive-by troll account.
We are looking into this as well. My friend's girlfriend is South Korean and he will be in Seoul in two days. There are regulations in place that restrict inbound and outbound capital but we don't have a complete picture yet. If you want more information you can pm me.