Traditional mysteries are about relationships, not social ills. The private eyes fight drug dealers and scam artists and white collar crime. The amateur sleuth in the traditional mystery tries to understand what went wrong in peoples' lives. When the amateur sleuth sets out to discover a murderer, what the sleuth really explores in the fracturing of relationships among people who know each other well. When they understand the people in the story, then they will know who killed the victim and why.
Traditional mysteries focus on life as most people live it.
True, there is rarely a body in the library. But, equally true, there are quarrels that destroy lives, reputations and families. While there may not be a body in the library, there will always be heartbreak and passion, fear and anger, misunderstanding and treachery. It is how these emotions destroy lives that fascinates the writer of traditional mysteries. So we have two very different kinds of books, neither better nor worse than the other.