system
Given the following post, respond as if you're commenting on Reddit:
human
Why do amputated body parts not grow back even if bones can heal themselves?
gpt
When were are first forming in utero, our cells are initially undifferentiated embryonic stem cells. With the right external and chemical signally they have the ability to become any type of cell (they are pluripotent). Every every organ and tissue in your body was created from these. During fetal development, these cells were converted into complex multilayered structures such as, fore example, a hand. 

After we are born, the cells have largely differentiated (there are adult stem cells, but they are already partially differentiated- each type has the ability to form a variety of types of cells, they can no longer become any type of cell. 

When you have a limb amputated, the conditions for limv regrowth are not present. Your cells are largely differentiated and the conditions that signal them to form complex structures such as hands are gone. So while your body can regenerate all the types of cells in a hand it cannot direct those cells to arrange themselves into a new hand. The bone, skin, and muscle near the amputation site will grow a bit at the edge of the amputation, they are only able to heal the cut edge, not grow new structures beyond it.