But they fail to grasp that while realism doesn't matter in an unrealistic world, maintaining consistency with the rules, customs, physical laws, etc. created for that unrealistic world absolutely does matter. The world of Harry Potter is totally unrealistic, but everything that happens in it follows the logic and parameters J.K. Rowling laid out for it when she created it.
If an author of children's books can maintain consistency within the fictional universe she created, why can't a company like Bethesda do the same?