Answer: One of the reasons why it is illegal is that it is an advantage over the poorest and most vulnerable groups of people.
Explanation: Selling a kidney is part of what is known as "organ trafficking," which involves the removal of an organ from the body for commercial purposes. This activity is considered illegal in a large part of the world.
It is illegal to sell my kidneys or any other organ of my body since these practices take advantage of vulnerable and poor groups of people, where they obtain a profit well below what the organ is actually worth. Apart from this, selling an organ poses a health risk since it is in the body because it fulfills a function for its proper functioning.