Probably a similar reason to why there are tournaments and ranking systems exclusive to women in chess. From my understanding, there are far fewer women in chess than men, more hurdles for women in chess and less opportunity for them to thrive and reach their full potential. Many may have started later and were generally less encouraged to pursue chess, likely resulting in less time spent playing chess from a younger age. Therefore there are events exclusive to women in an effort to create a more balanced competitive environment that isn’t dominated by men who were placed in front of a chess board and cheered on since they were in diapers.