Oxford English Dictionary
reductive 2.c. Relating to . . . the interpretation or reanalysis of something in simpler or more basic terms; simplificatory; (in later use freq. depreciatively) reductionist, characterized by excessive simplification.
Study of literature and humanities develops critical thinking that recognizes and comprehends complexity and the mixed nature of human existence in moral terms.
Put another way, such critical thinking rejects overly simplistic, black-and-white or absolutist thinking. (e.g., "My way or the highway"; "No way, Jose"; "You're either with us or against us.")
Any human intellect is constantly tempted to shut down on the complexity of reality and to see the world in reductive terms of us & them, good & evil, interesting & boring, etc.
Training in literature, humanities, and critical thinking at least helps one become aware of these tendencies and to "reduce" their impact on our thought and behavior.