Why does Crooks allow Lennie to enter his room?

When Lennie appears in Crooks' doorway while checking on his pup in the barn. Crooks tells Lennie to go away, but the simple big man cannot understand that he isn't wanted. Crooks at last relents and allows Lennie to sit with him and talk.

Lennie had moved into the room again. Crooks scowled, but Lennie's disarming smile defeated him.