They aren't but they should be. Many lives could be saved by making gun safety a mandatory class for all US students. If every kid had to learn the basic rules of gun safety, a significant number of accidental deaths could be prevented, and even many not so "accidental" deaths could be prevented because people would immediately recognize when someone else is being unsafe with guns. And gun safety rules are good things to ingrained in peoples heads when they are young. Similar to other safety rules like don't run with scissors, or put your seatbelt on, or don't pull sharp objects towards your body, or look both ways when crossing a road. If you teach it to kids in a serious manner the safe actions become a reflex action.

And part of the problem is that our entertainment media (movies, shows, video games) pretty much trains anybody who has not been taught gun safety in real life to reflexively point a gun at somebody when it is picked up, often with their finger already on the trigger (although some movies are better about this now). People see a gun on the ground, may not even know its real and think its a toy, "Hey guys look what I found" and immediately aim down the sites at their friend.