There is plenty of literal language in Of Mice and Men. The book largely deals with Realist and Naturalist themes; the descriptions of characters and landscapes are often straightforward. Also, George tries to speak directly and clearly to Lennie so that Lennie can understand him. Figurative language might be too confusing. Lennie also speaks literally; figurative language is a little over his head.
However, there are examples of figurative language. In Chapter 2, George asks the swamper why Curley is so abrasive. The swamper says that Curley is "handy" meaning that he is always trying to start a fight, ready to use his hands. Curley keeps one hand "soft" for his wife. He defines himself by his hands because they are his means of pleasing his wife and his means of working. This repetition of hands and being "handy" establishes hands (ranch hands) as a theme. When Lennie crushes Curley's hand, he limits his "handiness."
In Chapter 4, Crooks says, "I seen too many guys with land in their head. They never get none under their hand." Crooks has seen plenty of guys who dream of owning their own land. But none have ever actually gotten it.