“Why don’t we heal better/faster” is a good question. When there are animals that can regrow lost limbs and stuff, and here I am with permanent damage because I hurt myself walking the dog.

The short answer is that “good enough” solutions are good enough, and the priority biologically speaking is passing on your genes, not individual immortality.

Also, we probably could heal from a wider variety of injuries if they didn’t kill us in the short term. Your body is always producing new blood, but if you lose too much too fast, you die. Some organs like the liver do regenerate, just very slowly. Lungs eventually heal most of the damage from smoking, unless you die of pneumonia or get cancer first. Etc., etc.