Billy as a character

The writing style of this novel doesn't give the reader a chance to fully understand Billy as a character. We have read snippets about Billy's childhood, read about his job as an optometrist, and heard about his strange interactions with his war comrades. Some of the Billy's memories that we read seem to be random and sometimes unexpected which makes it hard to figure out Billy. In many other books, the reader is able to learn and connect with the main character within the first 50 pages of the book, but all throughout this book I find myself still trying to understand Billy as a character. In class when we read The Grapes of Wrath, we were able to quickly learn about Tom Joad. We quickly learned that he was recently let out of jail, he's faithful to his family, connected to his community, and a hard worker. All of these qualities are personal things that made it easy to connect to Tom, but the main character of Slaughterhouse Five, Billy, is quite different.
When Billy was in the hospital after his plane crashed into Sugarbush, few people came to visit him. Another patient who shared the room with him said, "'He bores the hell out of me'" (pg 184). Even in the war he was not appreciated or liked at all by the other men. He even told them to "go on without me" because he knew that he was not wanted (pg 156). When he traveled with his comrades on the train, they wanted him to "keep the hell away from here" (pg 79). So, at many different points Billy was clearly not accepted by other people. However, it is hard to understand why he wasn't accepted since the reader was never able to fully connect with Billy and understand him. It is hard to imagine what he does to make people hate him so much.
Why do you think Billy is not liked by many people? Why was Billy chosen as the main character of this book if he isn't a "likable" person? Do you think that the writing style of the book contributes to how much we are able to discover about Billy?