As someone who has spent time in Iceland I can tell you it is very homogeneous due in part to its physical isolation, and a wariness of outsiders that borders on xenophobia. They are very friendly to visitors but it is difficult to move there and - other than possibly in Reykjavik - outsiders are socially isolated.
The other factor is the near 100% literacy rate (Icelanders study four languages by the time they are out of secondary school), high degree of education, internet use, and civic engagement. When we had problems on an isolated road, people came out of the woodwork to help us and would not accept any payment. We were told this is just what people do for one another there.
Our society by comparison has approximately 20% of adults who are completely or at least functionally illiterate and close to 40% who read below a fifth-grade level. These people are for the most part completely disengaged from the political process with the exception of sound bytes they hear on TV or talk radio.
We also have a culture that suggests that we should not concern ourselves with civic matters, distrust strangers and our government, and achieve consumer "success" whether we can actually afford it or not, even at the expense of others. The fact that the media is largely controlled by the same interests who benefit from the rest of us not knowing what is going on is -- in my opinion -- not an accident.