Well, they humanize history. Instead of just dry facts, we see the past through the eyes of fictional characters who are living in that historical context. Take 'Roots' as an example. It makes the experience of slavery in America more relatable and understandable. The details about daily life, like food, clothing, and family structures in historical fiction books help us piece together what life was really like in different historical periods, which is something that pure historical texts might not always convey as vividly.