Most basically, because there wasn't an "Emu War" in any literal sense. It is a somewhat tongue-in-cheek description of the failed pest-eradication campaign in the fall of 1932. It is counterfactual, but had it been declared a success, we most likely never would have heard of it, let alone would be calling it the "Emu War". For a more in-depth explanation of just what was going on, I would refer to this older post.