It's really strange how close Papa New Guinea is to Australia (by territory, not people to people) and how little contact there is between the two countries, and how little interest there is. Australians couldn't tell you a thing about PNG, its people, or its politics (except those few who've gone to PNG for mining jobs). Compare with New Zealand - NZ is further away by continental distance, but closer to the main cities of Australia. Completely different relationship.

Not that strange, actually, once you understand the geography and ethnography. First of all (although not that significant), straight line distance between the population centres of AU and PNG is further than that of AU and NZ: Sydney to Port Moresby ~4 hours by direct flight, Sydney to Auckland ~3 hours. More significantly, the whole ~1000km length of Cape York Peninsula is one hell of a barrier: virtually uninhabited, no sealed roads most of the way, and extremely inhospitable (cyclones and mass flooding for several months every year, killer crocodiles / jellyfish everywhere, prevalence of dengue fever / malaria).

The Torres Strait Islanders are genetically and culturally part of the peoples of New Guinea, which is why here in Australia we refer to "Aboriginal and Torres Strait Islander peoples", why the TSIs have their own flag that's different to the Aboriginal flag, etc. We non-indigenous people of Australia and New Zealand share the same predominantly British ancestry, a very similar (and intertwined) colonial / post-colonial history, etc.

Are you aware of the Australian indigeneous ethnic group called the Torres Strait Islanders? They are considered ethnically distinct from Aboriginal peoples in the rest of Australia. There are about 100,000 of them. They reside on the islands between the north tip of Australia and the south coast of Papua New Guinea. Thus, I would qualify your post by saying: The vast majority of Australians have little contact with PNG, but the Torres Strait Islanders have had contact with PNG peoples for thousands of years.

You can learn more about them here: https://en.wikipedia.org/wiki/Torres_Strait_Islanders

It’s of interest certainly but why would it be strange that Australia, a member of the Commonwealth and New Zealand, also a member of the Commonwealth have closer ties? The US has closer ties with the UK than it does Cuba, for example.

Isn't it still hundreds of kilometers from the mainland?

The straight of Gibraltar is 10km and barely any Europeans have anything more than superficial knowledge about North-African cultures.