@Zeus is the father of the gods in Greece. He knows full well who Kratos is and fears that he one day will come for him after making him kill his own family.
Zeus betrayed Kratos primarily out of fear that Kratos, his own son and the new God of War, would overthrow him, continuing the cycle of patricide he himself committed against Cronos. Kratos's growing power, destruction, and defiance, coupled with prophecies from the Fates about a warrior destroying Olympus, made Zeus see Kratos as a threat to his throne.