the Chaldeans had arrived :

It seems almost certain that the reason is that by then the Chaldeans had arrived with their barbaric names for the planets — Nebo, Ishtar, Nergal, Marduk and Ninib. The Greeks simply substituted their own deities’ names for the foreign ones — so today we call the planets by names that are English renderings of Latin translations of Greek translations of the original Babylonian ones!