Japan had an industrial base... well, it had to in order to engage in a long fought war of attrition in all of the Pacific controlling and subjugating very large portions of the population and land area.

So they had an industrial base. No so much for (S) Korea and VietNam. They were very agrarian (like Japan before they built up their war machine). So their problem was peasant farmers with no land + a growing population on the brink of starvation.

US advisors made recommendations to alleviate this problem by doing land redistribution for tenant farmers. South VietNam would have none of that. Korea did appease the peasants albeit reluctantly so they avoided the worst.

That's actually a really interesting point. South Korea was actually steamrolled by the north, because the US made sure they had no independent way of defending themselves. The US pulled in the UNSC to fight on their own in Korea, while the Soviets had built up a strong local military in the North. Taiwan is now incapable to protect its own borders. They even had a nuclear weapons program in response to mainland China which the CIA infiltrated and shut down. Another example of a local military that was just steamrolled by an insurgency was the Iraqi military.

The US has a pretty good track record when it comes to building insurgencies though, remember that the Taliban were built and trained by ISI and the CIA. Iran had islamic groups that the Shah used to silence opposition forces. There's no way their training and equipment wasn't done in coordination with their US partners given how much of a puppet the Shah was. Or take a look at a lot of the groups that were part of the opposition in Syria.

I wonder if there's any analysis why the US has been so good at building and training insurgency groups, but so bad at making local armies to protect their own territorial borders.

Those treatment is thanks to fear of communism, and war vs communism. https://en.wikipedia.org/wiki/Reverse_Course