According to Guns, Germs, and Steel, why did the Australians not develop things like metal tools, writing, and political societies?
The answer to this can be found in Chapter 15. There, Diamond tells us that the Aboriginal Australians did not develop these sorts of things because they were unlucky in terms of geography.
Diamond says that Australia was really not very well suited to developing agriculture on its own. He cites two major problems. First, he says that Australia is inhospitable because of its dry and unpredictable climate. Second, he says that there are very few domesticable wild plants and animals. Since there were so few plants and animals that could be domesticated, and since the climate was not great, it was not possible for agriculture to develop. Because agriculture could not develop, the things that you mention could not develop either since they can only develop in agricultural societies.