Yet our bodies have excellent self-repairing facilities (as always, supported by appropriate diet, sleep, yada yada).
As the recipient of 2 knee surgeries, and possibly an upcoming 3rd, believe me when I say that I would like nothing more than to have my knees "self-repair". But it just isn't going to happen naturally. You get one set of cartilage and ligaments, and once they are gone, they're gone.