The reason they switched is that New Zealand dominates the south pacific as both the largest donor of aid and also the biggest trading partner to most of the pacific countries.
About 60% of cars imported into New Zealand are used cars, and New Zealand doesn't manufacture any cars. By the time a car has finished its life in New Zealand, it ends up on a scrapheap. There is no appreciable car export industry in NZ.
If you Google search for "Car imports Samoa", the first page is entirely websites exporting cars from Japan.
Do you have a source on that? All sources I can find show Australia providing about 5 times the aid as NZ. About what you'd expect given respective populations.
I don't have the numbers of total contributions, Samoa was historically an NZ protectorate and there are 144,000 Samoans who live in NZ who send a big chunk of their pay checks home, they also send a lot of money back to Samoa through the Samoan church groups.
I tried to find the information on the total flow of money from NZ to Samoa but the only things that I could find was the official government aid of $22.3 million, which compares to $35.8 million from Australia, but the aid from private citizens would be massive.
Auckland has the largest Polynesian population in the world and for quite a few pacific islands more of their citizens live in Auckland then back in their homelands, people are expected to come here and work and send all of their spare money back home.
The reason they switched is that New Zealand dominates the south pacific as both the largest donor of aid and also the biggest trading partner to most of the pacific countries.