A serious injury that limits mobility is certain death from starvation for many or most species. Adults of most species don't feed each other. This is true enough that finding a body or fossil with a healed fracture of a long bone is very interesting as it implies something about social behavior.
That's such a horrible death. Nature is brutal. One would wish there were a kill switch if you knew you were both in pain and going to die of starvation. Having that might even save some of your species members so that predators can't guess where the rest of the healthy ones are.
It's also strange that social behaviors didn't evolve in more species. They seem to have the brains to migrate thousands of miles and borrow homes, yet they don't have the brains to help members of their species, which would help them proliferate.
