English(lang) is the problem.
Korean and English have very different grammatical structures. I can read English in real time, but writing, listening, and speaking are difficult. (Maybe it'd be different if I were more proficient, but I've never lived abroad, so that's how it is.)
Because of that, remote work usually requires speaking, so most interviews end in rejection. I can communicate through chat, but the vast majority of employers want interviews.
And as the IT industry has grown and become more established, Korea has developed its own standards that diverge from global norms. This makes Korean IT hard to sell globally. I try to follow global standards, but in Korea, I'm told I'm using 'wrong technology' or doing 'over-engineering.'
Either way, the technology you learn or implement is often quite different—because the market leaders set the technical standards.
So independent developers in Korea have to learn both Korean IT standards and global standards—on top of English. (This is extremely painful.)
So if I could do remote work for a foreign company, it would be really, really great. But in reality, English is usually where things fall apart. Koreans often praise Korean as a 'scientific' language, but for most Koreans, it actually acts as a shackle. On the other hand, it's also because of this language that the domestic market is able to maintain at least a minimum level of viability.