It's the odd and distinctive feature of all cultures in Dune; nowhere, in any of them, are there concepts such as democracy or human rights. Even the 'nice' Great Houses, such as House Atreides, are feudal dictatorships, albeit relatively enlightened ones. Duke Leto treats his subjects well out of a sense of noblesse oblige rather than any concept that they might have inherent rights.

I'm lucky enough to have a copy of Willis McNelly's Dune Encyclopedia, once a semi-authorised companion to the Dune books but, since the interminable prequels and interquels published by Herbert fils, now relegated to the status of fanon. In an entry on the ancient history of humanity, McNelly implies that Dune and its immediate sequels are set in the future of an alternate history where Classical civilisation never fell and there is no history of democracy as we know it; it's been Emperors and Nobles since time immemorial.