One factor is “cultural flux direction”. As a Norwegian, I can understand Swedish very well, but Swedes do not generally understand Norwegian well to the same level. The languages have many similarities, but also many notable differences. But because Sweden always has been a cultural big brother to Norway, with a lot more and better books, movies and TV shows produced, Norwegians have consumed much more Swedish language than the other way around. And that kind of mechanism quickly becomes self-reinforcing.
I image it is easy for the same thing to happen in other parts, with other similar languages.
Latest Answers