Why are the The Guerrilla Girls important to (contemporary) feminist art history? They write, "Why haven't more women been considered great artists in the history of Western art?" Why is that significant to feminist art history?

The Guerrilla Girls exemplify the trend in contemporary art towards the critical and curatorial. As an activist performance art group, the Guerrilla Girls use subversive, interventionist techniques to point to gender and racial inequality in art institutions, like museums, galleries, and more recently, in art education. The group solidified out of a protest action in 1985 against the Museum of Modern Art, New York exhibition International Survey of Sculpture of Painting that purported to be the most comprehensive and up to date exhibition of contemporary artists that featured 143 men, 14 women, and no people of color. The anonymous, subversive -- which is to say guerrilla -- tactics of protesting in gorilla masks with plastic bananas spurred the name "Guerrilla" Girls.
Their art interventions take the form of posters, installations, and performances in the form of lectures and protests. The copy of their posters often asks provocative questions like "Do women have to be naked to get into the Met? [Metropolitan Museum]" The Guerrilla Girls' institutional critique was directly inspired by the advent of feminist art history, especially the questions posed by Linda Nochlin's watershed 1971 article "Why Have Their Been No Great Women Artists?" Her text posited that the lack of representation of women in art history and institutions spoke not to any lack among women artists, but to systemic inequality. Their posters are attributed to the collective, and performances are performed anonymously. This serves both as a reference to the institutionalized invisibility of women and other marginalized artists, but also as a deflection of the idea of the individual artist genius, who has most frequently been recognized among white men. Instead, they often adopt the pseudonyms of important women, which helps refocus attention on the inequality they are protesting.
For more information, see
https://www.guerrillagirls.com
http://www.getty.edu/research/special_collections/notable/guerrilla_girls.html

The Guerrilla Girls are an anonymous group of feminist activist artists. About 55 people have made up the group since it started in 1985 when its members took to the streets wearing gorilla masks and carrying posters.
The Guerrilla Girls are extremely important to feminist art history because they were one of the first groups to point out the inequities in the arts scene. Many of their posters are considered art in their own right.
Their goal was, and still is, to raise awareness about the underrepresentation of female artists.
The group have since organized protests, lectures, art installations, and performances across the world, visiting London, Paris, Madrid, and Istanbul, to name just a few.
The idea that not many women have been considered great artists in the history of Western art is significant to feminist art history because it uncovers prejudice and discrimination based on artists' gender. Because the majority of art critics are male and because most of the historically praised artists are male, many female artists are unknown or under-appreciated.
Thanks to the actions of the Guerrilla Girls, many of these underrated artists are finally receiving some recognition.
Something to be noted is that the Guerrilla Girls' choice to remain anonymous is a nod to the many women artists of the past that were made invisible.
Today, the Guerrilla Girls continue to work to expose the gender bias within the art world.
More information on their story can be found here, and a chronology can be found here.
https://www.guerrillagirls.com/chronology/

https://www.guerrillagirls.com/our-story/