There is a level of respectful dress that applies to all those created in the image of G-d. Married women covering their hair is a specific Jewish requirement.
“Why? There is no Chiyuv to move in order to avoid women who are in a (partial) state of undress.”
For most of us that may be true, for those who feel that they are overwhelmed by a woman not dressed to Chasidic standards – they should move. The pitfall of the daughters of Moav per Rashi really affected only one tribe. Others have great desires to take what does not belong to them. For them learning a good way to make Kosher money and living where plenty of Kosher money can be earned will keep them away from sin.