How is south Asia possibly not "big enough - it's literally based around the most populous country in the world! But yes, obviously logistics and friendly regulatory regimes are a big part of it. (FWIW I was including China/Japan/Korea in "SE Asia" in my post. Obviously all three have now developed beyond the good sources of cheap labour that they had started out as in the last 50 or so years. But there are still other plenty of potential candidates to follow the same path, both in Asia and elsewhere in the world).

They said "either"

    Japan and Korea have plenty of domestic manufacturing.

This is industrial policy, not free markets. Both countries strongly encourage domestic manufacturing (including farming / food production) through a wide range of social pressure ("lifetime employment"), tax breaks, tariffs, and regulations. There is no doubt that a lot of that manuf could be moved to much cheaper countries, which would enrich a few, at the expense of many.