There are a bunch of reasons from tradition in terms of letting sheep roam free to farming always having been a source of power. Further you have other weird facets like the votes of people in the countryside being worth twice those in Reykjavik. But basically for a long time farming and fishing controlled a lot of voting power. Although the traditional party of the farmers is on the wane now. The whole country has the population of a medium sized town so it’s on the whole very similar but also very different to larger countries.