It's because the gender loonies invented that word. You're using their language.

Think about it. If you call females "cis women" and trans women just "women" that's erasing women.

Just say "woman" and if you want to be explicit use "female" or "biological woman". That way trans women stay trans women.

By the way you don't need to politicize if someone calls themselves or their friends cis. Just say you yourself won't like to be refered as cis.