> In absolute terms, Japan and India have costs similar to South Korea

That countries like Japan and Korea have similar absolute costs as India which has a 4-5x lower PPP adjusted GDP per capita suggests that the price for labor for nuclear power plant construction is globally set (relatively few qualified engineers who can demand a high price), or India uses a lot more labor, or a combination of both.

India probably uses a lot of foreign expertise. It’s either the French or the Russians that supply the reactor. That would change in the future I suppose and cost would drop. Also, corruption.

India was under nuclear sanctions until recently and had to build and design everything from scratch. Every component is made in India for PHWR which adds a lot of cost, due to r&d and economies of scale. Also, India is still not a member of NSG, due to repeatedly being blocked by China.

Japan ceased all construction of nuclear reactors in response to Fukushima daiichi, and since that was a decade ago I'm betting that all the competence they built up has disappeared.

In other words, very similar to what happened in the US in response to Three Mile Island: after a scary nuclear incident there was a lengthy pause in nuclear construction which meant that all of the skills and learning-by-doing that had accumulated up to that point went away, and starting again would be significantly more expensive and subject to massive schedule and cost overruns.