Why do certain cells of the body divide at different rates

Because different cells of the body need to reproduce faster like blood cells because if we didn't have them we would die, or when your growing your body is getting rid of old cells and replacing them

Because some cells in the body are subjected to a hostile environment and may die. Skin cells are one example of this, and they rapid reproduction. Brain cells enjoy a relatively calm environment and hardly divide at all. Hope my explanation made sense.