Why is cremation regarded as an irreversible process?

Cremation reduces the body down to its basic elements, destroying all organic matter so that all that remains of the body is inorganic mineral elements and bone fragments. With burial, you can exhume a body and still extract identifying information, even though natural decay processes are present. With cremation, you cannot extract any identifying information from the cremated remains of a person, nor can you distinguish between the cremated remains of one person from another.