According to Guns, Germs, and Steel, why did the people of Australia not develop metal tools, writing or complex political systems?
In Chapter 15, Diamond tells us that Australian natives did not develop these things because of their bad geographical luck. The geography of Australia did not allow for agriculture and a lack of agriculture meant no large societies that could create such things.
Australia had no domesticable animals since all large animals were made extinct when humans arrived. It had bad soil and is the driest continent. It also has a very unpredictable climate. Diamond says it is hard to make modern agriculture work well in Australia and so it would have been essentially impossible to make it work with what the Aboriginal Australians had.
Because they couldn't farm, the Australians couldn't have dense populations, which are needed to give rise to things like tools, writing, and complex political systems.