The problem the developed world is running into is that more and more people realise that life can have a better quality without kids. In Germany especially this doesn't have much to do with wages or working hours. Germany is actually pretty good in those areas and the laws and regulations are very accommodating if not outright supportive of starting families.

Young women these days also have much better career prospects than they did a few decades ago so a lot of women chose to focus on their career and staying single because why wouldn't they.