I think it could be possible that these elements are deliberately blacklisted too, as a device for subconsciously creating a mythic atmosphere. Legends don’t talk about restrooms or toilets on Mount Olympus, for instance.
If this hypothesis is true, that device would only work for one or two films; at most a trilogy, because in the course of detailed full-universe exposure over time, it becomes extremely conspicuous. Children’s cartoons might be able to get away with it, like there probably were no bathrooms in Voltron either, but adult cinema, scifi or no, is a different matter.