I don't think homework is meant to educate the student. It is meant to help push repetition and mastery of concepts. It is likely very difficult for most students to master physics, mathematics, or other quantitative subjects with just 5 hours of instruction a week in person (and the large class sizes in the US and other countries probably don't help).
I disagree slightly (explanation below), but whether you take "educate" to mean some sort of deep exploration or just rote repetition, I think the the point still stands.
The disagreement comes from n=1 anecdata drawn from my own education, but after 8th grade or so nearly all my homework was designed to complement rather than reinforce in-class instruction. Picking on mathematics as one of the things you mentioned, the in-class instruction would introduce a concept, and the homework would give you the opportunity to flounder a bit and probe the bounds of that concept. I particularly enjoyed questions like "the author made a mistake in this question; how would you correct it to be answerable?" In some sense that's repeating a concept, but when you're doing something more than repeating the same technique over and over there's a sense in which it's different too.
