At least in the past many mustelids were often thought of as difficult animals to exhibit due to stereotypic behavior as well as being very prone to escape. This has probably changed now due to advances in husbandry, but it could explain why we don't see more of them in zoos. The fact that many are nocturnal might also make some curators hesitate.
Its no wonder mustelids shows sterotypic beheaviours in human care, because most zoos are keeping them still in too small and boring cages. Nuremberg Zoo changed it and has build a large, very well outdoor exhibit for the Sibirian Martens.
