The fog of war is a real thing and I am sure plays a part. POS reports need to be given religiously, but sometimes they're not relayed properly to the air officers, FSCC, etc.. All it takes is someone getting a grid off by one digit, either by fat fingering a keyboard/keypad or stuttering on the radio. The speed at which troops can move can make POS reports just a few minutes old completely invalid too. Pilots then see troops just a few hundred yards from where they think friendlies are, and the unthinkable happens. Add to that the incompetence of some people, even senior enlisted men and officers/company commanders, etc.
It shouldn't happen in the open desert, but does. I am sure it happened in Vietnam and the South Pacific even more often, due to the pilots not being able to see what they're firing at, and the lack of precise coordinates provided by today's GPS capabilities. Same with urban operations.
I've seen both GMLRS and 155mm artillery rounds go into the wrong places, due to all of the above. Luckily all the times I saw it happen the rounds landed in random areas and no friendlies got hurt.
