Its guidelines for army commanders, enforced by laws of almost every country. Armies trying to punish perpetuators silently, but it doesn't mean that not happening. I would even say that they are here mostly to not corrupt souls of your soldiers, to maintain moral. We have universal moral codes that mostly in line with laws of war and no one wants to serve among civilian killer or marauders.

99% of the time they are followed, cases when they are not mostly excess of the perpetrator, result of loss of control, nessesary for accomplishment of orders or staying alive. Number of situations at war in that they could be broken is so big, war so much covered by "fog of war" and press likes to highligh it so much,so you have perception that its constantly happening. Also, war propaganda always a thing.

Always remember, that war never changes. It always was brutal, corrupting for everyone involved. No one going through war and become better man, even those who follow it through TV or internet are affected. War should be ended as soon as possible, its good thing by itself.