In of Mice And Men, why are all people shown as animals with little or none humanity? Do they not dream or compete like what humans normally do?

I don't think they are shown as animals. The characters feel isolated and alone. Like all people, they need to feel wanted and to belong. Even Curley is isolated in his own head. All his issues come pouring out through displays of aggression and violence. The characters do dream. We get ring side seats to the dream of a little farm for Lennie, George, Candy. We watch their dream as it comes crashing down with a bullet in Lennie's head.