Because they are still slaves of their nafs and that "feeling" of being looked and appreciated by males. Married or don't married doesn't make difference to them.
Unfortunately this is a malady which has affected also many sister with "stylish" "fashion" hijabs with make-up and un-modest clothing.
Again that same "feeling" is the culprit here too.

We muslims Alhamdulillah are told that all that is of true value is our piousness. Whereas all that a non muslim knows is that who & what they are is whats matters. Which means are they good looking enough, are their clothes nice, do they have a fancy car, a big house, a phd degree, lots of money and power - thats what defines them.

This is their principle : "god made women beautiful so if god did not want their beauty to be seen why make them beautiful? beauty must therefore be shown to be seen otherwise how will people that you are beautiful & appreciate gods creation?"

We believe on the other hand that everything is created in a certain way for a certain purpose and its upto us to follow the Divine law to make use of every thing as it should be used.

The other thing is we believe Quran to the word of ALLAH, they believe religion is man made. Therefore according to them its the plot of 'men' to dominate woman & keep her to himself.

We exist in a certain state of mind & they in another. Therefore surah AL kafiroon. last ayah : "you have your deen & I have mine" Your belief dictates your life including the way you dress. If you believe in something different then you will dress differently.

And ALLAH knows best

Perhaps it is not that - perhaps it is simply them taking pride in their appearance and wanting to feel nice when they're out in public? I for one am a young female and I wear a little makeup and a nice outfit every single place I go. I prefer to smell nice, look nice and feel nice when I am in public because the way people present themselves says a lot about the way they live at home and their hygiene. I have learned this through personal experience.