It occurred to me that the were two reasons, and for those who aren't familiar with one of them, it might be good to mention it.
The first I think everybody knows: unless it's a life & death situation, you do not shoot toward/near another person. Period. What if the game/target or the other person moves as you fire?
The second is a bit more involved, that being the amazing ability of just a touch by something to deflect a bullet. Remember that a bullet is not only moving forward at high velocity, it's rotating at very high velocity, and when the two are combined with even a slight touch of a twig/branch or whatever, it can cause the bullet to go places you never intended.
I've known two people who fired a shot at deer in brush and missed. Relatively short range, so they were checking very carefully for blood, hair or anything else that would show they'd hit, and they found where the bullet had clipped a branch or twig they hadn't seen.
A few years back I read an article in a magazine where a guy decided to test this out. He built a frame and stuck 1/4" and 3/8" dowels in it running vertically and spaced around so a shot fired through it would have a good chance of hitting one. Then he set a target about five or six feet behind it, backed off a ways and fired a number of shots. Every one that hit a stick, even just brushing it, was deflected off target. Some actually missed the paper entirely, as I recall. I can't remember the proper scientific explanation, but it does happen.
Now, there was no brush between me and the deer, it was an absolutely clear shot. But the deer itself has muscle and bone. The 8mm load I worked up would, at that range, completely penetrate the deer, no question it'd lose a lot of velocity, but it would go through; and if any of the bone it passed through deflected the path...
May not have actually been a problem, but the risk was one I just wasn't willing to take.