Husbands and fathers are responsible for their families and must also learn the Halochos of Tznius. They are also responsible in ensuring their wives and daughters dress according to Halacha.
How can a Jew consider himself Torah-Observant if he does not correct his wife or daughter if her method of dressing is immodest and violates the Torah, as established by Chazal?
Especially if he sits and learns Torah all day.
Believing in the One G-d is a Mitzvah of Yiddishkeit. Keeping Shmiras HaLoshon is a Mitzvah of Yiddishkeit. Keeping Kashrus is a Mitzvah of Yiddishkeit. Keeping Shabbos and Yom Tov are Mitzvos of Yiddishket. Keeping Taharas HaMishpacha is a Mitzvah of married Jews. Covering the Head is a Mitzvah of married Jewish women. Keeping the Mitzvah of Tznius is a Mitzvah of a Jewish woman. It’s all a package deal.