They are bottom of the food chain prey animals. Like mice, rabbits and deer. They evolved to run away from predators, and reproduce fast enough to make up for the loss. And, if one get taken down or falls while fleeing from predators, it should fail catastrophically. This way the predators stop chasing the others. If 3 horses get injured fleeing, that's 3 horses that will die. If one gets injured and fails immediately, the others are saved and the heard is better off.

Rabbits have a literal suicide mechanism. When a hawk grabs a rabbit their hearts explode before the hawk can even carry it off. Because a rabbit wriggling away only to die on the ground can mean another healthy rabbit gets nabbed to fulfill the same meal.

They are the glass cannons of running away.