In my story, the Humans did not originally have princesses. One young lady happened to come by that title by virtue of the "enchanted princess" fable, consigned as she was to suspended animation in a whitebox.
It was the Dragons who had a Royal pattern of rule, with Dragonlords controlling and defending large territories.
By default, in accepting the hospitality of these Dragonlords, (in exchange for services being rendered. Humans can allegedly be useful.), the Humans also accepted and mirrored their form of social order, a medieval one.
In this wise, we get swords and machines, flying dragons and soaring rockets, primitive transportation and interstellar battles.
Ah, the Sleeping Beauty.
Her name forgotten by the living, found by accident among the ancient relics, and possessing knowledge the descendants of the survivors do not have.