In fantasy and science fiction, authors build worlds. If the world an author builds differs in every way from our world, he has a lot of explaining to do. And explaining is almost always boring. So the author should not make things too different from our world.
Everybody knows what a cow is. In a fictional world, maybe there are not any cows. But maybe people do eat meat in this fictional world. And either they catch meat wild or raise it. If they raise a big meat animal, it serves the same purpose as a cow.
So if you create a fantasy world, most of the time you will use cows and not gups and most of the time you will make these animals cowlike and not guplike (gups have a hive mentality with intricate survival activities performed by each gup that allow the gup colony to survive).
In a science fiction world, you are more likely to have gups than in a fantasy world, if you even mention such things--maybe food comes from a Star Trek replicator. In any case, the author must limit the number of gups or else the story gets bogged down in details.
The sci-fi author might call a world's cows its "domesticated herd animals," and save the explanations which might try the reader's patience except for things that are essential to the story and/or interesting to learn.
If the heroes are going to use the ship's hyperdrive to cook galactic pancakes to sate the appetite of MindlessWorldEaterGuy, the author might explain how they convert the hyperdrive field into thermal energy.
Interestingly, Jules Verne, who has been called the first science fiction writer, wrote books that were more like travel guides full of gups (in space, at the center of the earth, at the bottom of the sea, etc.). More precisely, Verne took people on tours that involved science that they most likely did not know.
But readers have grown up since Verne--they got tired of characters praising Hovlafazor and passing the roast gup. Readers don't mind if the characters praise the Lord and pass the pot roast, as long as the characters set their phasors on kill.