Masks work dramatically better when the person wearing the mask is the one who is sick. A grocery store where the one infected person is masked is better than the grocery store where the one infected person is openly coughing around 30 masked people. Everyone masked works best, but the heavy lifting is done by the sick persons mask.
In short; You wear a mask to protect others from you, not the other way around.
However, this creates a severe social stigma problem however: People wearing masks are outing themselves as being sick (whether or not they actually are). The result is people don't wear masks for fear of social retaliation.
So now you, as a scientist, have to figure out what the messaging around masks is going to be. Wear a mask to protect others? Wear a mask to protect yourself? Everyone wear a mask all the time because we say so?
It was a damned if you do damned if you don't situation. They went with everyone wear a mask all the time, alluding to the implication of masking being a tool of self preservation. Of course masks don't work great at stopping you from getting sick (outside of being specially trained in their use), which is easily proved, and half the country recognized they were being lied too (while never acknowledging that the sick person wearing a mask works great).