Perhaps they have simply realized that no political decisions are without downsides, including unchecked immigration, and that on balance, they’ve decided it’s not for them?

It’s silly to claim that immigration is the only way to care for old people. We have been caring for old people for the entire history of the human race. We can start doing it again anytime.

It’s true, that it’s inconsistent to demand no immigration and simultaneously defendthe right to produce no children. But it is Japanese people who need to square that circle, not people who want to immigrate to Japan, nor people outside Japan, who feel Japan should allow immigration.