Koreans can use YouTube for streaming, it just isn’t the go to site for some reason. Most of the mainstream Korean content creators used Twitch because that’s just the site everyone’s used since the beginning and it’s easier to gain an audience there. For example, exKR mainly stream on YouTube, but when they did stream on Twitch their numbers were slightly higher, and that’s because more Koreans use Twitch to watch livestreams than YouTube. That’s going to change now obviously, but if people are switching over to Naver, then I don’t really see them migrating over to YouTube. Naver gets a lot of traffic, it’s sort of like Weibo in that sense, so people might prioritize the eyes already on Naver rather than take a chance at people finding them through YouTube.