Cis simply means not trans so they say.
It never even did, you know?
The researcher who coined the word, did so with the view that conforming to the sex stereotypes and sex role stereotypes associated with one's sex was healthy and rejecting the sex stereotypes and sex role stereotypes of one's own sex and conforming to those of the opposite sex was a sign of mental ill-health.
Of course, it won't surprise anyone that these researchers were men. Because women have always known that we lose out either way - if we do not conform to the stereotypes associated with our sex, we are punished by society. If we do conform to those stereotypes, we are diminished and limited.
That's because sex is the basis upon which women and girls are discriminated against and sex stereotypes and sex role stereotypes (aka gender) are tools used to do so.
The idea that women may be mentally well and still reject stereotypes simply didn't occur to the inventor of the word. One point in his defence - he was dealing exclusively with mentally ill males who identified as women and never even considered women. (No idea if it would be different if he had.)
So to a woman, cis never just means simply not trans, because there is so much more meaning woven into that concept than just a word.
As men who identify with the stereotype of women are really just expressing their preferences, i.e. expressing their personalities, we should treat this like all other preferences being expressed - there's a word needed for those who do. Not for those who don't. Much like we don't have words for those who don't collect stamps, who don't go spotting trains or planes and so on.