Why is it a good thing for countries to have high birthrates? We don’t need all the extra hands to work the land anymore. France and Hungary have tried to pay citizens to have more children and have failed.
Actually, those two and other countries have adjusted their system and are having more success with it now - earlier attempts did not take into account the prejudice against males in their family court systems, which had to be resolved.
It’s not that these countries need high birth rates, but that they need at least a *replacement* birth rate level, which is 2.1 children per couple on average. If your country is not overcrowded and you don’t need to reduce population, you still need to have replacement rates - otherwise, those countries that do have replacement or better rates *will* end up eclipsing and taking over your country. Japan is a great example of this - they’re looking at a demographic crash the likes no other country has seen since the Black Plague. Aside from the military and cultural preservation aspects (look at what happened to France in WW2 for why that’s a huge problem militarily) having a population reduction like this removes most of your country’s tax base and means you have to import people and that gives them power over you in the long term.