After paying taxes in Germany their net salary was less than what they had made net in Ukraine. Most of them went back.
This is insane. It overlooks quality of life: stable democracy, low perceived corruption (police, gov't, biz, etc.), economic stability, personal safety, food safety, social safety net (physical and mental healthcare, national pension, etc.), (industrial, economic, financial and environmental) regulation, quality of public education, quality of public transportation infrastructure, quality of publicly funded arts, income inequality gap, etc.
Income tax in Ukraine is about 20%. I used to live in Hongkong. Max tax rate was about 15%. Overall quality of life was terrible compared to advanced economies with 2x/3x tax rates. Sure, you might be "rich" on paper, but you pay a lot for privitised versions of these quality of life services. I always say: "If you pay little [in taxes], you get little [in gov't services]."
Another way to think about it: Look at countries that are not corrupt but it is very hard to get rich. Usually, those countries have excellent quality of life.
And maybe they went back for cultural reasons (food, family, education, etc.). I have observed that pattern many times.