Why is the last line of the novel, Of Mice and Men, a fitting one?

The last line of the novel is Curly's response to George as he and walks away, with Slim consoling him after Lennie dies. Curly says, “Now what the hell ya suppose is eatin’ them two guys?” This line is fitting because it contrasts Curly's lack of commitment to anyone with the devotion that George shared with Lennie. George and Lennie's friendship was stronger even than Curly's relationship with his wife. It is significant because it shows that self-absorbed people usually don't commit themselves to others or have strong relationships because they are too wrapped up in themselves. He is so inconsiderate that he can't understand why someone will mourn the loss of Lennie because Lennie didn't have anything that appealed to Curly. The line is also fitting because it was the way most of the world viewed Lennie. He was different, so most people thought he couldn't contribute anything, when in reality, he made a huge impact on George and eventually Slim.