If the community actively punished those who dress untzniusdik, it would have an impact and reduce the massive chillul Hashem and many other aveiros they do with this act, and even worse cause many others to sin.
Unfortunately (since there is no beis din) even though we can’t give her malkos for their public pritzus transgressions, as that would likely be most effective in reducing this crime, we have other avenues available to us. We could not give aliyos to husbands and fathers who allow their wives and daughters to go in public in a non-tznius manner. Or other potential punishments that can be utilized.