there are two likely reasons for that.

the main reason is that it's in korea. the korean market is closed to outsiders. no money can get in or out so the prices do their own thing and pretty much ignore the rest of the world because the rest of the world can't touch it.

even then that price is much, much higher that the other korean exchanges. this almost always means something is broken somewhere. i'll guess you can't deposit btg there. if coins could flow normally arbitrage would wipe that premium out. no one turns down free money.