It’s like in Unpretty, that 90s song by TLC:

you can buy your hair if it won’t grow

you can fix your nose if you say so

you can buy all the iPhones that MAC can make

Months are one of the best ways for a low-tech/pre-tech culture to keep track of dates (using the Zodiac for something it can actually do—act as a calendar you can see no matter where you are in the world).

Keeping them around is a sensible fail-safe in case some nuclear power sets us back into the dark ages.