They dont know exactly how far this virus can travel through air. People who cough spread the virus with power. People who breath out normally cover a small area. If you are nearby and inhale the virus you have a good chance to get sick.Maybe we already are. The CDC is recommending masks because they suspect it may travel more than 6' in the air, call it what you like that is airborne,.
Not many of us are infected yet. About half the population gets sick after infection. Mainly the 30+ / 40+ .The children and young adults often don't get sick.
Best way to deal with this is to spread the infections over a long period as long as there is no medicine available. Because many people need hospital care for pneumonia (oxygen). Hospital’s cant take new patients when full/complete.
This is going to take much longer than some presidents say / hope.