As someone mentioned, it's because Latinas rather than Latinos. Some people have used Latinx or something similar to denote both, but I saw some backlash on that and am not sure if it's preferee. Anyway, historically Latinos denotes either male or just general pop, kinda like mankind does in English.
Latinas on the other hand is specifically feminine, so it's like "mothers against drunk driving" type organizations, specifically named to signify that it's women. so they weren't being sexist, just responding to the specificity in like manner.