Because no law change is needed. The problem here is not the law, it is that politically correct, politically driven “leaders” are earnestly listening to any enemy who alleges any crime. They place the presumption of wrongdoing improperly on our men, not on a proven murderous butcher.
And they do it to placate naive people who sit around whining that soldiers should act like gentlemen, and that brutality should fit into legal niceties.
By your standard, half the USMC and US paratroopers in WWII should be prosecuted.
You are wrong. This was not a “political” prosecution by the military, at all. It was made political by the SEALS and their legal reps to save their hides.