The world chess federation FIDE recently made the incredibly transphobic and mysogynist ruling to exclude trans women from competing in women's tournaments, to strip trans men of pre-transition titles and to subject trans people to a two-year long surveilance process that could lead to forced outings. The German and French chess federation have now decided to ignore this ruling. Source in German (mostly with the info from the image): https://www.queer.de/detail.php?article_id=46744
The below are goodi answers, but the original answer was that men made it a boys only club and excluded women from competition into the late 1950s, so women made their own tornament.