A declining population puts immense strain on a country.
Apart from increased pressure on public spending as demand for healthcare systems and pensions rise, a declining youth population also leads to labour shortages that have a direct impact on the economy.
So the answer to the problem is to keep the Ponzi scheme going by bribing couples to have more babies - a lump sum at birth and then monthly payments up to 1st birthday - on top of the existing child benefits. In other words, keep the population growing. And don't forget importing labour - immigration.
Apply this thinking to all other countries and you can see why the planet has a problem. One day, maybe not too far in the future, the bubble will burst unless new thinking is applied to the whole issue.
Like it or not but new ways are going to have to be found and implemented to stop the incessant rise in populations.