There seems to be a strong connection between personal affluence and liberal freedoms and the number of children!
Well... millions left places like Romania, Bulgaria, and the Baltic States once those countries joined the European Community, or emigration restrictions were lifted.
Those millions were most often the youngest, most energetic, and of child bearing age.
The ones left behind were often older, less ambitious, with less to fall back on, etc.
You complain that Germany is in the same situation, but it clearly is not. I'm attaching below a chart of the four countries demographic history over the past half century roughly - with Germany first.
You can see Germany continues to grow, while the others have experienced a demographic collapse (10% is the smallest contraction). What Japan and Korea are dreading, has already happened to these people, and it's only accelerating.
But now there are millions of Romanian-Americans, Anglo-Bulgarians, Franco-Latvians and so on. Those countries losses, are Britain's, America's, and France's gains.
The best part - those people and their descendants will never come back, except for a few token visits to "see the mother country".
Russia didn't invade any of those places. The EU has pumped them with tens of billions of dollars. And yet - the result is evident to all. So please don't say Germany is in the same position.