Why missing personnel remain listed as MIA

Why can personnel missing after a battle remain missing in action rather than being declared killed in action decades later?

Because death cannot be confirmed without reliable evidence such as a recovered body, so the accurate administrative status remains missing.

The distinction is partly administrative, but it reflects a real evidentiary limit. Battle can inflict terrible injuries while leaving no confirmed account of what happened to an individual. If no one saw the person dead and no body was recovered, officials cannot establish death in action as a fact. Missing in action therefore records what is actually known rather than what later observers assume. Casualty categories can remain unresolved for decades.