Korea prices for BTC are at 22-23k... although coinmarketcap excludes that too (asterisk).
9 Bithumb BTC/KRW $219,098,000 * $22,052.30 1.38% Recently
46 Korbit BTC/KRW $76,213,200 * $23,244.90 0.48% Recently
70 Coinone BTC/KRW $46,977,700 * $22,992.90 0.30% Recently
The question is why would one exclude korean volume instead of factoring it in, with a corresponding percentage to their volume (versus the global volume). As long as the trades aren't zero-fee trades, the volume should be accurate.
certainly Bithumb has a lot of zero-fee trades
https://www.bithumb.com/u1/US138