Perhaps it was because he wasn't immersed in the story or his emotions weren't affected by the story. Crying is an expression of emotion, usually because the character has experienced something sad or painful that the reader can empathize with and react emotionally. When reading a novel, try to immerse yourself in the story, imagine yourself as the character, and feel his or her emotions and experiences. If she could immerse herself in the story, she might be able to cry. You can also try to adjust your emotional state, such as breathing, meditation, etc., to relax yourself and reduce anxiety and stress so that you can better understand and feel the emotions in the story.