For the love of God, I do NOT WANT TO KNOW.
It's also this incuriosity that makes it particularly lousy as a children's film. Anyone who's gotten on a bus with a second grader knows well the proclivity of man-larvae for the question, "Why?" One of the reasons behind the aforementioned trend of adults reading children's books is, I think, the fact that children's book authors are not afraid to answer this question, sketching out whole fantastical worlds with the resulting explanations. These worlds don't have to be realistic, but they do have to hold up under investigation -- to reveal causal connections, social relationships, customs, and habits that resonate and fit into the whole. In this sense, coming to understand the world of a story is an education in miniature for children who are at the beginning of learning about the order of our world. As I said in my previous post, the greatest strength of the original airbender show was the way that it rewarded the viewer for wondering about details -- about everything from the various nation's cultures to the flora and fauna of the wilderness. By comparison, the film isn't awful. It's just empty.