Change over in personnel from promotions, people leaving, or new recruits means that every few years or so you are looking at an entirely new armed force. While it seems simple getting troops point A to point B. It's a logistical and bureaucratic nightmare. By having war games every so often you make sure the Army has people with experience to accomplish the task. You also make sure that policy and procedures are honed and any oversights in the process are fixed. You also make sure that knowledge trickles up the chain of command as people from this year's war game get promoted.
It's about being vigilant.
My father was a radio operator aboard several different ships during WWII.
My brother was 2nd Mate on a ship during the Gulf War. He sat for 30 days off the coast of Japan...loaded with missiles.
The war games are just that.....pre-programmed games.