It also has to do with mild weather, access to resources like water and arable land, and a stable society. Although their biggest weakness would be inability to defend itself due to low population versus, for example, China.
China takes over countries using financial pressure (either through aid or financing loans) and broad pro-China deals (universities not being able to speak of Taiwan as a country, etc). Their MO is not generally invasions, so worrying about them is not sensible.
Location, stable government and real estate (ie asset parking) environment, ease of buying property as a non-resident.
Buying property on a small island to prep for climate changes seems... counter intuitive.
New Zealand is not a small island. It's bigger than the UK.
New Zealand also has a lot of relief. It is not an atoll which could be overrun by a 1 meter sea level rise.