The answer to this can be found in Chapter 15. It is very much in line with Diamond's argument in the book as a whole. Basically, Diamond says that Aboriginal Australians did not develop these things because they were unlucky in terms of geography. Australia was not a good place for agriculture to arise. There were not many domesticable plants or animals and the climate was unpredictable. Because of these things, agricultural societies could not arise. If agricultural societies do not arise, the things that you mention cannot develop. Thus, Aborigines did not develop these things because the geography of their continent was not conducive to agriculture.
The Aboriginal Australians suffered mostly from their geographic location, the environment and adverse climates. Although Australia had been inhabited much earlier and saw developments in stone tools and water transport, the people did not pursue these developments much further. The author attributes this stagnation to poor environment and harsh climates. The people were unable to develop their food cultivation and weapons. There were no animals to domesticate because by the time people settled on the continent most native mammals had become extinct. These challenges forced the Aborigines to become hunters and gatherers leading a nomadic way of life. The group was more focused on survival and kept moving around especially towards the wet areas of the continent. It is by their arrival to these wet areas that they began some form of land management and development of canals to enhance their fishing. The challenges that the Aborigines faced naturally impeded their progress and the decision to become hunters and gatherers was their only option given the circumstances.