The title says it all. Pretty much the only other cultures as primitive as theirs were(are?) Inuit cultures. If it just because they had to put so much time and effort into not dying because of the harsh dangerous landscape? I wouldn't think that's the case because not all of Australia is a desert. Even on Papua New Guinea, just of the cost, people there had large impressive structures. Surely after inhabiting the continent for 50,000 years an advance urban civilization could have developed.