This problem is not isolated to Japan. Countries all across the world are facing the same issue and have been for a number of years.
Create a shitty, miserable, society with no rights or support, and people do not want to bring children into it.... who'd guess?
The flannel has been wrung dry to the detriment of the working class; there is no where to go, no more water to squeeze from them. This is global society / capitalism falling apart.
Twenty thousand tons of ivermectin to Texas. Stat! That'll fix everything!