Nowadays we have nation states and boundaries. We have a buraucracy, publishers and broadcasters located in the capital that influence the language spoken in that country. 500, 1000, 1500 years ago it wasn't quite like that. Things were more fluid.
Älvalska descends from whatever was spoken there, which was presumably closer to what was spoken in Uppsala at the time than to whatever was spoken in Hamar (in Norway some way west of Älvdalen). But there wasn't a ban on travel to Hamar, nor a state that lent prestige to the dialect spoken in the capital.
Nowadays we have nation states and boundaries. We have a buraucracy, publishers and broadcasters located in the capital that influence the language spoken in that country. 500, 1000, 1500 years ago it wasn't quite like that. Things were more fluid.
Älvalska descends from whatever was spoken there, which was presumably closer to what was spoken in Uppsala at the time than to whatever was spoken in Hamar (in Norway some way west of Älvdalen). But there wasn't a ban on travel to Hamar, nor a state that lent prestige to the dialect spoken in the capital.