They could kill each other
Sometimes the greatest threat to emigrants was other emigrants. They shot each other in hunting accidents, or shot not-so-accidentally for looking at someone wrong. There was no law enforcement, and often no doctors. An axle might break, sending their wagon careening down a cliff as they carefully inched their way around the Rocky Mountains.
Broken bones and cuts were a common problem as people had to move and maintain their wagons and the massive beasts who pulled them. There was almost no protection from nature, disease, or from other emigrants, so it paid to keep your head low and eyes open.
