Why are there so many baha'i(s) on small pacific islands?
The country with the largest Baha'i percent is Nauru (tiny pacific island), then Tonga (same), then Tuvalu (same), then Kiribati (same), actually, here is a list
My guess is that this is a result of the fact that during the fifties and sixties Baha'is were encouraged to disperse throughout the world and establish communities everywhere where they were legally permitted to do so. While this might not have had that much of an impact on larger countries in smaller island states Baha'is were much more visible. Eventually even the king of Samoa (recently deceased) became a Baha'i.
In many cases, this is because of 'group conversion' -- where most or all of a village or extended family converts. Group conversion happens only in some more traditional societies. If it happens two or three times in a micro-nation, it shows up on the statistics. If the same dynamic happens in a larger country (it can, for example there have been group conversions among the indigenous people in North America), it does not show up in the national statistics, and the concentrated Bahai population disperses in a generation because even people brought up in a traditional culture are mobile where geography does not prevent it.
The responses from others here - that it resulted from a calculated dispersal of Baha'is to different parts of the world, or that it may have been group conversion in traditional societies - are okay as far as they go. These are, if you will, sociological explanations. But in another sense, it has something to do with the spiritual receptivity of different cultures to specific messages. The Baha'i teachings and the life of Baha'u'llah resonate strongly in various cultures at particular times. About a decade ago, Guyana had the largest percentage of Baha'i population of any country. And Baha'is expect that efforts to reach out to neighborhoods around the world and share Baha'u'llah's teachings with people who formerly were strangers, will ultimately result in questions like yours that ask: "Why are there so many Baha'is in Phoenix, Arizona?" Or in Sakhalin Island? Or in Patagonia?
As one of those pioneers who spent 8 years living on Pacific islands, I'd say the lack of diversions so prevalent in modern society was not present in the 50's and 60's. People had time to visit and converse. They also had time to size you up. The lives of the people were simple and human relationships were very important. Everyone has lots of relatives and it's important to keep track of how one is related to everyone else. So if one hears of this interesting new religion with a strange name, then the news spreads fast. It took time to translate Baha'i scripture into local languages and to help people understand the social and behavioral changes needed to build a Baha'i society. But some island cultures already contained Baha'i type cultural attributes such as the need to reach a con census in harmonious ways.
Why are there so many baha'i(s) on small pacific islands?
