Why is "terf" a term we use?

They aren't feminists. They're just your garden variety transphobes. Feminists want equality for the sexes. Terfs want trans people to not exist. It's not even related to feminism and any ploy of feminism is cognitive dissonance to try to give their transphobia a leg to stand on.

In short. Why don't we just call them transphobes? Calling them terfs implies there's some actual feminism going on here.