That's the point of Billy's time travel. Humans don't see the whole picture. Humans don't see the consequences and repercussions of their actions. The implication is that, if humans could see, or would think about, the whole picture, they wouldn't do things like bomb the city of Dresden, treat each other cruelly, etc.
Vonnegut uses the Tralfamadorian view of their lives, and Billy's time travelling, to demonstrate this point. Vonnegut was an atheist,