Why does Carlson ask the last question at the end of the novel?

Carlson does not comprehend the emotion behind Lennie's death as well as the kinship that Slim and George feel for each other.

Carlson asks the last question because it is symbolic of the fact that all the men on the ranch have downfalls. Carlson’s was lack of empathy and understanding of emotion and how much anguish George must feel after having to kill his best friend. This is also showed when talking about Candy’s dog, he doesn’t understand why Candy is so reluctant to give his dog up. Carlson’s question being the last line in the book reminds us of the truly depressing themes throughout the book, depression, loneliness, the fact that the characters cannot change. Lennie could not change.