If solvable, it is ridiculously expensive. For one, the cost (non monetary) of birthing is placed on just half of the population. So the other half needs to sweeten the pot for that half. And these divisions are not just men/women, but also old/young.

Second, the benefit of higher fertility rates is not seen for decades, but the drawbacks are immediate. So it is very difficult for the participants to agree on a price. Many will die before they see any benefit, but they will pay the costs.

Artificial wombs might be an answer, but I doubt they are coming soon.

>I think the importance of at least stabilizing the population is widely recognised, so I don't think it's the case that politicians are asleep at the wheel or something

I see it more as "we tried nothing and we're all out of options". Similar to how I wanted to lose weight for years and instead gained 30 lbs over the pandemic. You need to solve the underlying issues if you really want to fix the problem. And this problem seems to be cultural.

It's a similar situation to the US, despite having very different causes and consequences. But similar solution: give people time for leisure and don't work them to the bone during the physical prime of their lives. Which does mean "paying people the same for less hours", the kryptonite to corporations.

That said earth is beginning to self-correct so we may get there more violently than by the relative peacefulness of birth decline.

Problem is that not one country that has suffered declining fertility rates has managed to reverse the trend despite trying for decades. Not one.