Faulty premise. There are lots of series that are pretty close in style that aren’t made in Japan, e.g. https://whatnerd.com/best-non-japanese-anime-series/ (I just searched for “anime not made in japan” and this was one of the first results). There are also many Japanese animation studios who outsource some amount of work to other east-asian countries to save on costs.

And considering that manwha (Korean comics) looks exactly like manga, that’s exactly as expected.