Yep. Living near the sea means access. In three weeks you could go all the way from Bergen to Lofoten by sail. As soon as you set foot on land.. no access. Before roads and tunnels. Even recently.. the book "Three in Norway, by two of them" from 1881 was written by a couple of British guys (they were three, but two wrote the book) going to Jotunheimen for fishing and hunting. They left by ship from Newcastle and arrived in Oslo (today's name) after just two days, but going from Oslo to (at the map, "nearby") Lillehammer took three whole weeks. With support from locals and guides and there was even a road at the time.

My grandfather, who lived at the coast, could meet people up and down the coastline as much as he wished. But there could be people living just a few kilometers away, as the crow flies, who he would never meet.. because there was a mountain in between.

Thus, dialects along the coast have much more in common with each other for much longer distances than inland dialects which can vary greatly even over relatively short distances.