With all due respect. 20% is one of only two Tax Bands operating in Germany - the other being 0% - making it one of the very few countries in Europe operating such a scheme. Understandable considering that when it came into force, their State Mechanisms were in such a torrid state, it was the only system that they could operate at all.
In fact, it was precisely by making such setups so simple, that they were able to rebuild and recover - or at the very least, it constituted a major contributory factor. So is it any wonder that Germany, today, is referred to as the Home of K.I.S.S.
To call it 0% is over-stating it. There is a 5% rate, a 12% rate, and a 20% rate for individuals. The 0%-20% dichotomy is on their corporate tax side. The rate is 0% on the corporate side for for-profit businesses with fewer than 1,500 employees, and all non-profits. For-profit businesses pay 20% on their net profits.