It's certainly smaller than any American state, but for our population it's fairly big. The topology of the country also isn't very friendly to cell signals. 90+% of the country is mountainous/fjords. It's why coverage has been a big selling point, a bunch of people live on some random mountain side in the middle of nowhere.
From what I've heard, there isn't much competition in the US though, so I guess that plays a part. We got three companies independently building out their own network across the whole country.