Kalevala is from Finland which is not a scandinavian country and neither did it ever have vikings (only individuals who joined the viking raids).

The nordic atmosphere of darkness and coldness alongside the melancholy and depressiol it tends to create, is a pretty good breeding ground for some great metal. The nordics are also quite progressive so metal wasnt seen in the same quite negative light as elsewhere when it started emerging. Good connections to the world, enough money and free time and a active youth also contribute greatly.