The first response that one hears from teen girls when you ask them about tznius is “trauma.” This might be why: if one were to look at the focus of girls’ education it appears that the most integral mitzvot in the Torah are Shabbos, kashus and tznius. Which is interesting given the fact that tznius is not mentioned in the Torah itself, is referenced as a middah in Micha, and the guidelines that we follow today are only brought in the Gemara and later sources. Which is not to say that tznius isn’t an important halacha; I try to enforce tznius dress code for my students at school and it upsets me if any of my own daughters try to push the limits but… to be honest, tznius does take center stage in our education system far more than halacha affords it in Shulchan Aruch. Maybe this is because frum society tends to focus on outside appearances and it’s easier to “gauge frumkeit” this way.
There are many factors why teens push back. They are more exposed than ever thanks to social media on their phones and they want to dress like the influencers that they (strangely) idolize. Many are insecure and dress is a key part to their identity that makes them feel distinctive or helps them fit in. For whatever reason, tznius is a challenge in our generation and making it such a defining characteristic of frum Judaism doesn’t seem to be helping; if anything it makes it worse.
What’s the solution? I have an 280-word limit, so I can’t offer answers (if only I had them).