I found a fascinating article on the official Visit Sweden website. It was entitled "Why are Swedes so Stylish?" The most interesting part to me is that the article was more about politics and culture than the mechanics or history of good design.
As the article says, the Swedish aesthetic comes from the very Swedish concept of lagom, a word that translates roughly as "just right". That is a rough translation, too. A lot is packed into that one word.
Lagom has a strong social connotation. It means having just enough as compared to your neighbors, the idea that "I'm not OK unless everyone else is, too". It means avoiding ostentation or displays of consumerism. The celebrity culture, the consumer culture, that is so evident in the US is not nearly as strong in Sweden.
Another way to look at is the Power Distance Index, a measure of the "distance" between the powerful and less-powerful members of a society. Where I live in Texas, there are many gated communities; you need to be pretty wealthy to get in. I think there are very few such communities in Sweden.
The idea of having very little distance between someone powerful or famous and the average person on the street strikes me as a very desirable concept. The Swedish idea of "everyone being in it together" is one of the things I love so much about my adopted country!