I think problem is predicting how other side will react and then fitting that in your "game". Assume it's early 2003 and you want to prepare program for troops that will be stationed in Iraq after the war (the war hasn't started yet).

What will situation be like after Saddam is toppled? Who will be your friends and who your enemies? What methods will they use? Which way will population swing? And many, many more

The biggest problem is human behaviour. You simply can't reduce it to mathematical formula that will neatly fit into computer program. People act irrationaly, people act on different impulses than you expected, peopel work on different set of values etc.

I agree that computer programs are valuable for certain task, which are more or less mechanical and don't work on many variables. Say convoy escort. However certain task can't be simulated by computer. Say checkpoint duty.