Why are Roman keys found more often than Roman locks?

Roman keys are found more frequently than Roman locks primarily due to the materials used in their construction. While the Romans typically manufactured the locks themselves out of iron, they often crafted the keys from bronze.1

Because iron is highly susceptible to corrosion—a process where the metal reverts to a more stable mineral state such as iron oxide—many iron locks have deteriorated significantly or disintegrated over time when exposed to environmental elements. In contrast, bronze is more resistant to such decay, allowing the keys to survive in the archaeological record much more reliably than their iron counterparts.21