This is obviously colored by my own cultural perspective, but homeschooling is seen like hereditary debt. Children have a right to build a life free from "faults" of their parents. Allowing children to be removed from the public school system is very broadly viewed as leaving them much worse equipped for their later life, not unlike had they inherited crippling debt.

(And from having attended school in Germany — I don't see how any parent [or even group of parents] can teach a curriculum even remotely similar to a German high school. You'd need more than one person's worth of full time occupation just to prepare across history, math, geography, literature, chemistry, biology, foreign languages… a pupil can pick up 3 foreign languages in a German Gymnasium ffs! Are you going to put them back into public school if your child turns out to have a talent/interest for languages? Or math? We did basic integral calculus. Can you teach that?)