Maybe I have too precise a definition, but I think "didactic" should mean giving advice, and not just information. Almost all fiction is about psychological insight, but that isn't directly practical. And I don't mean "practical" in a daily life way: the reason I don't count Animal Farm as didactic isn't because I'm not a Bolshevik, but because even if I were, it still wouldn't tell me how to change the course of the revolution.