Or did the quick collapse of British forces in Malaya substantiate a belief that the Australians and New Zealanders would be easily defeated and later isolated? Would the abundance of resources, agricultural and growing manufacturing power that Australia and New Zealand possessed at the time as well as Japan over expanding into a frontline that was incredibly faraway compared to the defenders as well as rapidly depleting resources such as oil create any doubt that these smaller though developed nations could put up troubling resistance against the Empire of Japan?
After the collapse of Singapore, Australia and New Zealand were effectively isolated and while their manufacturing capabilities were developing, they were not capable of supporting offensive actions in the pacific. (in fact after the supposed threat of invasion had passed, Australia had drastically reduce their military buildup because they were unable to sustain it economically). The Japanese did attempt to isolate Australia and New Zealand further by capturing Port Moresby, Fiji and a number of other pacific islands. This would have cut both countries off from the United States, preventing the US from using Australia as a base from which to launch its offensives against the Japanese. The Japanese plan failed due to their defeat at the Battle of the Coral Sea and the successful defence of Port Moresby by Australian forces during the Kokoda campaign.