OP asked something different!
Arbitrage bots don't work when you can't get money out of an exchange you're doing arbitrage on and you can't balance your accounts!
That's why the kimchi premium existed, because of capital controls, it was nearly impossible to do arbitrage!
Back to the initial question, it's not about getting around capital controls but simply the lack of interest from Korean investors to pay that much compared to others, they got burned twice, the FOMO is no longer there, so there is no premium anymore. Add on top of this the constant regulations, the fact that you no longer can withdraw coins to non-verified external wallets and you get the picture.