Answer:
1- The author did not add details about the cyclops, so as to not make the tone sad after he is harmed, by making us like him first. It would not only be sad to like the cyclops, but we would resent the one hurting him as well.
2- The author left out details about the sheep, seeing as they’d take away from the adventure and the excitement. Among all the exciting things we encounter in the story of Odysseus, reading about sheep is hardly one of them.
3- The author omitted details about Odysseus’ fellows as to not add too much sadness to the tone. Reading about their stories and lives would've been nice but, like in point one, it would be sad (and the reader would feel upset) because as they die it would be like some sort of joke.