Lennie's mental disability makes him into a child, he is really immature.He's a little kid trapped in the body of a big man. Innocence may protect Lennie, because he never has to deal with the reality of what he's done.
Lennie loves animals, but kills them; Candy loves his dog, but can't stand up for it. In the natural world, love has nothing to do with safety.
George and Lennie don't call each other 100 times a day, and they don't like every single instagram picture the other posts on but they still get the sense that they take their friendship more seriously than anything. A real friendship where loyalty is predominant.