Perhaps because the vast majority of Americans have never ever seen nor heard the word Niqab?
I certainly had not prior to reading this Q and I think I’m pretty well read about Islamic culture and live not that far from Dearborn, Mi. which has the largest population of Muslims in the US. NEVER EVER encountered the word Niqab.
And for whatever reason , when there arise disputes over Islamic women’s covering (such as certain job situations or Driver License photos) the covering is most frequently referred to as a veil or as a Hijab. I dare say that there are far far more people aware of the word Hijab compared to the nil amount of people aware of Niqab.
When women cover the majority of their face with any type of cloth in any type of culture they are VEILED (not Niqabed).
When a bride covers her face even with the skimpiest of lace coverings, she is considered veiled even tho most of her face is clearly visible.
Veil is a pretty useful generic term for a face covering of any sort and I have yet to hear a Muslim saying “Excuse me, but its not a veil. It’s actually a Niqab ”
So that’s my guess on why people aren’t using the precisely exactly correct term. The word veil (or even Hijab) gets the job done adequately since everybody pretty much understands what is being talked about. There really is no ambiguity.
And if a Muslim would ever make the effort to explain to me when I’m using the wrong terminology , I’d thank them for the new info., get clarification about the nuances of which word applies when and adjust my terminology accordingly just to be polite.
So far, in my personal experience, that hasn’t yet happened so I really don’t know whether its that much of a major big deal or not.