The paper says, "Of course, high-IQ societies exist, but then most of their members appear to be rather successful and hence limited in their understanding of people who never achieved much, if anything, in life."
Some people join high-IQ societies because they haven't achieved a lot, and any society where they share an important attribute is a place where they can fit in. And Mensa, at least, has a good deal of support for gifted children.