If there's an epidemic starting, then only a small number of people have the disease. Everyone wearing a mask would help, but if you have a limited number of masks, you want to focus them on people likely to have/catch the disease.
The masks worn by people without the disease would be ineffective or even counterproductive if health care professionals were missing PPE as a result.
The masks worn by people without the disease would be ineffective or even counterproductive if health care professionals were missing PPE as a result.