From Tuoi Tre News:
Foreigners’ disdain for face masks worries Vietnamese

...anyone who's been to Asia knows that these surgical face masks are everywhere.  This was true even before the corona virus.  (I remember almost 20 years ago getting into debates with my Japanese co-workers over whether or not the face masks did any good in preventing colds.)
But it is something that the locals believe in.  Which is why I've started wearing them everywhere myself now, just to try to ease the mind of the people in my host country.
And who knows? Maybe they do some good.