Because a piece of cloth is not going to stop you from being exposed to or infected by a virus....
Pure and simple... Masks are simply theater.
If you want to mandate everyone wear an N95 mask at all times, fine.. but even that doesn’t stop a virus 100%... and most places the “mask” requirement is a joke... here’s a bandana... or an old shirt tied around your face... that’ll teach that virus.
Its theater, nothing more.
The New England Journal of Medicine calls them magic talismen