Answer:
Because of the remoteness of Oceania, and the difficult landscapes, especially in New Zealand, this region of the world, and its nations, were only approachable to any other country through sailing. Originally, Oceania was mostly inhabited by Polynesian tribes, who were seafarers, and that is one of their common origins. However, given distance, and difficulty to mainatin contact, soon many common factors of these tribes, began to differentiate.
In this case, there was a lot of cultural isolation, which permitted the aboriginal peoples of these lands to remain so, until the British first arrived in Australia in 1778 and the Dutch arrived in New Zealand in 1642.
Up to that point, the culture and lyifestyle of these nations had remained pretty much closed up. But with the arrival of European powers through the sea, including France and Britain, a process of cultural diffusion initiated, including the exchange of languages between the colonizing powers and their new lands, and the cultures, and the political styles, of the two sides, also began to mix.
In present day, cultural isolation in Oceania continues for some of the left aboriginal tribes that were initially on the region, but cultural diffusion is a permanent thing, with languages, cultural systems an social systems acquired from the colonizers continues to be the major framework for all of them.