Compared to Australia, New Zealand has a significant Maori / Polynesian population. If you combine a part of Australia with a part of Fiji, you would get simila

Compared to Australia, New Zealand has a significant Maori / Polynesian population. If you combine a part of Australia with a part of Fiji, you would get similar mix of people and also a similar economic output to New Zealand. While this obviously doesn't explain all of it, it is important to consider the historical and demographics reasons as well.