Homeschooling has ALWAYS been banned in modern Germany. (As it was in America until about 30 years ago...).
The Germans are too afraid of radicals (that would be neo-Nazis and Islamists) bringing their kids up in isolation without integrating them into the larger German society...
Given their history, understandable, in my opinion.
Homeschooling was outlawed by the Nazis. They kept the policies.