What is the difference between galvanization and sacrificial protection?
They are used in different media. Galvanization is used to protect iron exposed to non-corroding medium (air), while sacrificial electrodes are used to protect iron in electroconductive and corrosive medium (sea water or moist soil).

Protective zinc oxide layer on galvanized surface is desired to stay undisolved,  while the purpose of sacrificial electrode is to keep being oxidized to assure electron flow to other metal surface. In latter case medium electrconductivity is a must for ion transfer process, while corrosivness is needed for oxidized zinc surface layer disolution.