Cremation is the doing of the Hindus and not the Muslims! Our Prophet salla Allahu alaihi wa sallam ordered us to wash the deceased and to bury him after offering funeral prayers! He told us that honoring a deceased is by hastening to bury him.
If he ordered his body to be thrown to lions at the zoo to feed on, would that have been ok? If he asked his family to keep his body in his bedroom until it decomposes, would anyone respect his wish?