… There were, however, some societies, like those in the Pacific, which developed in extreme geographical isolation, since less than one percent of the Pacific is land. For hundreds of years, the Pacific sat apart from the major trade routes and so the cross-fertilization of naviational ideas was limited. One result of this was that the unique navigation methods that were developed in the Pacific remain distinct and different to this day. –Tristan Gooley, The Natural Navigator
The Pacific is also the last (major) region of Earth to be settled. We figured out how to survive on the polar sea ice thousands of years before we figured out long-distance ocean navigation. Humans didn’t arrive in New Zealand until sometime around 1250-1300 AD, (which means they got to Hawaii and Easter Island–one of the mot geographically isolated places in the world–before New Zealand.) Or to put it another way, less time passed between the Maori settling New Zealand and Columbus arriving Cuba than between Columbus and the American Revolution. (This is even more remarkable when you consider that humans arrived in Australia 40-50,000 years ago.)
The short version of all of this, as we’ve been discussing, is that the Melanesians (who, as their name indicates, have a lot of melanin,) spread out along the southern coast of Asia following the Out-of-Africa event, settling in the Andaman Islands, modern Indonesia, PNG, and eventually Australia.
After that, they basically stopped. The distances between their islands and the next islands were too great for Melanesian technology, and the islands they had were probably pretty nice compared to taking their chances out in the open waves just to hope they might make landfall on some tiny speck hundreds or thousands of miles away.
About 32,000 years later, a group of Taiwanese folks (probably also descended from Melanesians,) developed some better boats and navigational technologies and set out to discover the Pacific.
(Interestingly, they also went in the opposite direction, across the Indian ocean, and settled in Madagascar.) The Polynesians who eventually landed in New Zealand are among their descendants.
Getting to Indonesia does not seem to have posed much of a problem for ancient man, since Homo Erectus got there even before h. Sapiens, a good 1.5 million years ago. Lower sea levels probably made this easier than it would be today, by linking up a lot of the islands to the mainland.
(I believe Indonesia is actually located on a sinking magmatic “cool spot” that is essentially drawing the whole region downward, leaving only the tips of its mountains above water; southern Africa is located over a rising magmatic warm spot, lifting the crust in that area.) But the movements of large chunks of crust across the mantle are beyond our temporal scope; we just want to know what Indonesia, PNG, and Australia looked like during the Ice Ages:
This still requires boats to cross, but it’s not too complicated a voyage. New Zealand, though, is right out. You’re not getting to New Zealand this way–the ocean currents are against you. I suspect it’s easier to get to NZ from the middle of the Pacific–as people actually did–than from Australia.