We never seem to see people complaining about what nuns wear, which I find to be a double standard.

Different context. Nuns wear their costume when they are serving. That's why you don't see nuns in full dress at Walmart.

But I see women in full burkas (always with their husband, of course) struggling in everyday situations.

If the religion requires it, it's a terribly oppressive one. These women "chose" not to face consequences, so they wear it. That's why there are international protests by women who call to reject these fabric cages.