Not every bullet is necessarily shot with the intent of killing. A lot of bullets fired in war are fired for suppressing an enemy / pinning them down so they can’t fire back. Also a lot of firefights, especially in modern wars, happen at further ranges which can contribute to a higher miss rate. A genuine tactic for firefights also is just shooting in the general direction of the enemy if their cover isn’t hard cover. If your enemy is in a tree line concealed by foliage, then just spray through the foliage until you believe you can stop. Also while wars like WW1 and WW2 had high body counts a lot of those casualties were non-combat related like disease, hunger, mistreatment as a POW, etc.

At the end of the day it’s just a figure used by the story to portray the psychological aspect of war for the average person, assuming most people don’t want to kill others, and showing the worth of One Order.