[h_mirin]

Especially in recent years, public infrastructure investment is evaluated by ROI (though not just from an economic perspective). Therefore, if the population declines, the number of projects meeting the ROI threshold may also decline.

Also, I live in Japan and can perhaps provide an example:

In Japan:

- Public infrastructure investment reached its peak in the mid-1990s.

- The birth rate peaked in the mid-1970s.