> because they lack prefabrication-level standardization
It is not the only reason. Another reason is too many regulations and unpredictable government. As a private investor, you get lower ROI because you'd need spend several years fighting bureaucracy with no predictable outcome, and after the project started, it can be shut down in a couple years.
This is true for almost any energy project nowadays. EPA regulations change and bam, you're out of business.
> too many regulations
I don't think there's "too many", but I'm very far from an expert on this. What seems evident is that a prefab reactor/plant can amortize the cost of getting approved, whereas template plants, like the AP1000 are unique every time, even if they are fundamentally very-very similar, they are not identical. Hence the need for going through all the site specific differences, and their effects on the whole system.
It is not the only reason. Another reason is too many regulations and unpredictable government. As a private investor, you get lower ROI because you'd need spend several years fighting bureaucracy with no predictable outcome, and after the project started, it can be shut down in a couple years.