WHAT ABOUT THE MIA"S

Can someone please tell me why the USA has'nt gone after there MIA's - Can they still be there??? Its worring that as a ex-Soldier myself that if i had gone to War and was MIA I'd Hope to God that someone was looking for me and i would not give up hope.. I'm just trying to understand......Please any INFO would be Greatfull.

Ex-Australian Army...