Unexpected best-sellers

According to THR, Scandinavian production companies Zentropa and Nordisk Film are working together on a film version of Frans G. Bengtsson's 1941 novel The Long Ships. I was surprised there was much of a demand for a cinematic adaptation of 1940s adventure story set in 10th century Sweden (particularly one with such a pulp fiction-y cover), but Wikipedia informs me that this is actually a super-popular book in Sweden, where it has topped library lists of the most-borrowed books for years. (Still: the Swedish winters must be ridiculously long.)