I think it is because they believe in Jane Law.
http://en.wikipedia.org/wiki/Jante_Law
There are ten different rules in the law as defined by Sandemose, but they all express variations on a single theme and are usually referred to as a homogeneous unit: Don’t think you’re anyone special or that you’re better than us.
The ten rules state:
1. Don’t think you’re anything special.
2. Don’t think you’re as good as us.
3. Don’t think you’re smarter than us.
4. Don’t convince yourself that you’re better than us.
5. Don’t think you know more than us.
6. Don’t think you are more important than us.
7. Don’t think you are good at anything.
8. Don’t laugh at us.
9. Don’t think anyone cares about you.
10. Don’t think you can teach us anything.
An eleventh rule recognized in the novel is:
11. Don’t think there’s anything we don’t know about you.
In the book, the Janters who transgress this unwritten ‘law’ are regarded with suspicion and some hostility, as it goes against communal desire in the town to preserve harmony, social stability and uniformity.
Interesting.