Sweden has 10 people per mile of road. The US has 30 people per mile of road.
Sweden simply does better, despite having to deploy more infrastructure to provide service.
Sweden used to have a state telecom monopoly which then became the incumbent. You are right that regulatory capture has played a big part in the development of the telecommunications sector. Sweden had a strong incumbent, but that did not stop the municipalities and power companies from building out competing fiber networks, nor stop the regulator from acting in the best interest of the people.
So, the big difference was that the Swedes had both political support for building fiber networks and a more can do attitude towards getting things done, without excluding large parts of the community.
You can't really treat an entire region like it has a uniform population density, either. Area is not the relevant unit of measure, but total linear distance of the edges of the spanning tree.
Maybe a more predictive measure for networking costs would be median distance to nearest neighbor?