World creation is also one of the reasons we read. We want to know what life was like in, for example, C18th Paris, or Barcelona in the Spanish Civil War. We want to imagine pretend worlds, such as that created by Tolkien - how many visitors to New Zealand are really hoping they're going to end up in The Shire?
We like world creation as readers, and it's part of the writer's job to re-create a world, whether imaginary or real.
What sometimes happens is that the writer gets carried away by their world. Every little thing, every tiny detail gets given the same loving focus as the main features. If writers are sensible they keep the marvellous details out of their main works, and publish them separately eg The Silmarrillion by Tolkien, or Quidditch through the Ages by JK Rowling. Tolkien and Rowling are both wonderful story tellers and they know that too much detail weighs the story down.
So fantasy novelists have to guard against adding just the right amount of detail - enough to create a fantasy world, not enough to get in the way of the story telling. Any novel which involves research has to watch out for this too - social history is fascinating, but will your description of the manufacture of manglewurzel cutters add anything to your story?
And even contemporary writers have to guard against the temptation to describe every little thing in detail - I once read part of someone's short story that spent two whole pages describing a bureau and its contents, none of which was really relevant to the story but had taken up about 500 words. That's a high percentage of a short story to spend on 'creating atmosphere.'
So if your short story or novel appears to be endless, try going through and marking with a highlighter pen essential bits of action. Then be ruthless and cut the rest.