Why does a skin cell divide more often than a liver cell?

Skin is covered by epithelial cells. Liver is mainly made up of hepatocytes though fibrous and fatty tissues are also present. Cells of skin epithelium are present in different layers. Lower most layer on basement membrane (all epithelia possess this barrier on which epithelial cells grow) are newly generated. These cells gradually acquire a protective protein keratin but loses vitality. Thus by the time cells reach top most layer of skin they are all dead cells.