[snowwrestler]

More practically speaking, most parents do not have the breadth of knowledge to spontaneously tutor their kids in every subject. Homework can provide fodder for parents to engage with their children on academic subjects the parent might not know well, or might not think to bring up.

I know some people are taking offense to your comment, but the reality is that even parents who very much wish to be involved in their child's education often need a nudge on what, exactly, to talk about.

Even parents who home-school their kids usually buy academic materials to use for this reason.