Health-
Perhaps a simple limud zechus:
From the Gemara in Rosh Hashana (18b) it comes out that when the Jews are being ruled by the non-Jews but there is no ????? ??? if Klal Yisroel wants to fast they do and if not not. The reason we all fast today, brings the MB, is because Klal Yisroel has accepted upon themselves to fast. Perhaps the “minhag” of these segments of Klal Yisroel came about because they hold that the women never accepted upon themselves to fast, similar to what many say about ma’ariv.