Because in order for the ignorant gamers to understand where it was, you'd have to have all the people riding kangaroos or hunting koalas. Pity really, because Australia has some lovely scenery, both in the Outback and elsewhere; seriously you could make a Call of Duty game based entirely in the country and still have all the levels featuring completely disjointed scenery in far apart locales. ANZACs in Gallipoli wouldn't be too fascinating a game because you'd spend 90% of it in a dirty little trench getting blasted by both Ottoman and Allied guns, with the occasional 'over the top' bit during which your survival is calculated by the probability of survival rather than your skill. Then at the end, in order to satisfy the Hollywood gamers, time travelling Nazis would have to arrive with giant robotic spiders or something because overall, the campaign was a rather depressing failure. Still, Australians and New Zealanders in South East Asia during the Pacific Theatre of WW2 would be interesting, if only so its not the USMC (seriously getting sick of their prevalence in any game that has the Japanese and WW2)