“Why do we see every healthy healthcare worker wearing a mask?”
The PPE medical professionals wear is always as much to protect you from them as them from you. Think about pre-op procedures. They’re not doing that to protect themselves.
The vast majority of healthcare workers don’t routinely wear masks of any kind under ordinary circumstances (nonsurgical...such as floor nurses in a hospital), so it’s obvious they’re wearing them specifically because of the virus. If they’re not infected, they’re not protecting patients from the virus.