your question is of course natural and intuitive...but there is a simple answer.
modern day feminism is not about feminism...it is part of an 'alliance' of groups who hate white people and white civilization and seek to destroy it. (see: intersactionality)
this includes angry women, queers, non white races, jews, some atheists, etc.
This is in fact part of liberal ideology itself. This is not like some 'conspiracy' theory from me.
So a terf is someone kindof admitting that they dont necessarily hate white civilization. THey might even respect beethoven or shakespeare.
This is blasphemy for intersectionalists and the left in general.