I think the authors choose to limit those voices because they are not the most important. What the main character is feeling and their actions that they put into play, keep the story going. The supporting characters then respond to what they do by reacting in some way (whether it is good or bad). For example, in "Parents' Night" by Nancy Garden, when Karen admits to her family that she is lesbian. Her father won't except the fact that she likes girls and ignores her for weeks. He wants to pretend he has a "normal" daughter and is ashamed of who she is. Even though the dad has a big impact on Karen, and the book could have been written from his point of view, it is not the most important.
The effects on the stories that have a side, or many sides excluded, is that you don't get the full story. The reality is, a book can't have ALL different points of view. There are main characters and supporting characters. The supporting characters usually cause the problem and/or help the main character get over it. You may need to assume things or infer what a character is feeling. In the short story, "Michel's Little Sister" by C.S. Adler, Michel and his sister are really close. They tell each other everything and look out for each other because that's all they have since their mother is working 24/7. In the beginning, Michel's girlfriend--Wendy--breaks up with him because she thinks he is gay. "Forget it," she told him. "You don't want me, Michel. I don't turn you on." (Pg. 151) Later, Michel's little sister gets in trouble in school. She doesn't tell you why it is, but you can guess that it was something said to her about Michel's sexuality. You can assume this because of two things before that that are said. First, Wendy breaks up with him because she thinks he is gay. Second, a guy comes up to him and asks him out (figuring out before Michel that he is gay). Not having all points of view cause you to have to think more deeply about each of the supporting characters. You have to think about the main character too, but a lot of it isn't a mystery because they give it all away.
In some short stories, the main character's voice stands out because the other are missing. Therefore, you only know one point of view of the story and have to go by what is given to you. Most of the time, this is not the case but in the short story "Three Mondays in July" by James Cross Giblin, it is. The main character David, goes to the beach one day to discover some guy who is later known as Allen undressing himself. He is fascinated by his body and keeps on staring. When Allen realizes this, David runs away. You don't know how Allen is feeling, which only makes what David is feeling stronger. You have to assume that Allen is pretty mad and maybe freaked out. David is feeling confused about his feelings towards the old man and decides to come back the next couple of weeks. He is hoping to see if he can see Allen again, but he doesn't know why he wants to. This is an example of when David's feelings stand out because you don't know what exactly Allen is feeling.
I think that if you knew what Allen was feeling or if it was his point of view, the story would be completely different. He would probably describe David as a stalker and as a young boy, even though he is 17. You could get in his head although then David's point of view would be fuzzy. I think that the author made the right decision to put it from David's point of view, since this is David's problem.
Books are interesting because a point of view is always missing. If we knew what everybody was doing, thinking and saying in book, it would be quite boring. The mystery is what I like so much about books. I think that as we grow older, the mystery becomes bigger and bigger in books. I can't wait to read and discover more about characters in depth as I grow and develop more as a reader.