If I knew how to solve the problem, I'd have proposed it. Yet, this is certainly a political issue. As populations decline, the smaller and smaller generations will be asked to support older generations, keep government services afloat, and so on. If nothing is done, at some point, the advanced, post industrial societies will become poor agrarian societies, infrastructure will decay, and governments will collapse. Then, people will begin having large families again because they will have no choice. Farms need hands.