I wouldn't want fall damage, hostile animals, or the possibility of dying in the game either. But I could see the use of having skill point reductions/burning through extra calories if the player is exposed to pollution. It would create an additional incentive to manage it carefully. Also, in case you didn't know, the ecosystem overall is based on western North America. That's why there is the specific set of fauna. So lions wouldn't be an option (unless down the road they make one for Africa), and although bears could be an option, the world size is probably too small to support a population of bears.