Why can't you receive a hair transplant from a cadaver or another person if you are a good match?

Extreme depression is another reason why you should not consider hair transplants from a cadaver.The risk may be more depression.  Perhaps seeing a psychiatrist may help you cope with the depression.

Your immune system would reject the new hairs unless the genetic makeup of the hairs were 100 percent identical (ie an identical twin). Theoretically, you could be put on immunosuppressive drugs to block rejection but the potential risks of these drugs is considerable. Risks include drop in blood counts (sometimes serious) infections (some serious) kidney disease, mood changes like depression, and long terms risks of cancer for some drugs. Thousands and thousands of patients around the world have side effects from immununosuppressive drugs every month that cause them to be hospitalized. Unfortunately, some of these patients die. Bone marrow transplants are also potentially serious with many possible risks, including death. It is important to understand that a bone marrow transplant involves many risks and is reserved only when their is a high chance a patient will die without it.

Having extensive experience with MD Anderson training and seeing many transplant patients, I can tell you no transplant from another body is without its risks. This is true even with exact matches.

You can only transplant hair from an identical twin as we have done twice, otherwise the hair will be rejected. See web reference below

It is possible to have hair transplants from another properly matched individual but this would require suppression of the recipient's immune system. This is risky but reasonable for a life saving organ transplant but not for cosmetic reasons.

To supress the immune system is only worthwhile if there is a life threatening medical condition. Thin hair, even if the patient is suicidal, is no indication for what you propose.