>>719254328
It's the wests war on fun, that's why. Many regions would ban the game or give it a higher ESRB rating which would reduce sales. It's worth noting in the original Fallout 1 & 2 you could kill children, and you would get "Childkiller" reputation, making pretty much everyone hostile against you.
Barely anyone really cares about killing children in games, but it's the fact that you COULD if you WANTED to that increases player immersion and makes the world feel more alive.
Conversely in games like Fallout 3 when you shoot a child and they don't die, you're pulled out of any semblence of the simulation and are reminded that you're playing a game.
That's why many older games have stood the test of time because coming from tabletop RPGs, the game design philosophy was to simulate a real fantasy world as much as possible.