I think the Israeli experience is a big warning sign that everyone wanting to blame economics has it wrong. It's come down, but it flattened in the 2000s and remains strongly above replacement. You see the same in certain demographics elsewhere in the rich world.

It's culture. We (in the west) have created (and exported) a culture that undermines the family and family values, tells people there's things that are more important (or in the past, that kids were to be actively avoided), and then we try to talk about dollars instead when that leads to what it has. That reveals part of the problem; our hearts are focused on money, not the family, but money isn't the problem, we are.