I don't love the eternal question "Is this homework? We don't use the answer but we need to know whether or not it is homework."
Why can't we have a Q&A site for educational programming where everything is homework?
Primarily because "homework" is not specific subject of study to build a community around. A "Homework Stack Exchange" would be a catch-all site to ask about virtually any subject; a place where users go because of why they're asking rather than what subject the question covers.
That isn't how we scope out sites, essentially the same reason as: Why isn't there a general Stack Exchange?