It stems from an unhealthy approach to tznius; perhaps from an attitude which completely misses the point of tznius.
Having said that, I also don’t understand the animosity and hostility directed to Burqa wearers. People treat it like a cardinal sin, when to my eyes, it’s not that bad. To me, the reaction is totally exaggerated.
My limited view notwithstanding, the Gedolim have (apparently) come out against it.