Washing hands, avoiding touching your face, and other measures like these mainly help with what seems to be a far less common vector of transmission via surfaces and physical contact, where the virus only remains active for a very short time.
Droplets in the air are a transmission mechanism but only for short range (3-6 feet) and only a danger from people who cough or sneeze on you. Respirators are effective at stopping that transmission but they are most useful for people treating the sick. But they aren't effective if worn improperly. For most people, avoiding the sick is enough.
Surgical masks are useful for the sick to keep cough and sneeze droplets from spreading. They are also useful to keep people from touching their face.
The current understanding is that the transmission mechanisms for Covid-19 are:
1. Contact 2. Droplets (particles > 20 microns), AND 3. Aerosol (particles < 5/10 microns)
The last one - Aerosol transmission - really adds to why this virus is so infectious.
Unlike balistic droplets, an aerosol plume can stay in a room for a very long time after someone coughs or sneezes. An aerosol plume can stay in the air long after someone flushes fecal matter down a toilet.
As a comparison aerosol transmission is what makes tuberculosis and measle so challenging in terms of containment and infection rate.
For example, a quick google of "how does coronavirus spread" brings up this article as the top result: https://www.livescience.com/how-coronavirus-spreads.html
It says:
"The new coronavirus spreads mostly through person-to-person contact within about a 6-foot (1.8 meters) radius, according to the Centers for Disease Control and Prevention (CDC). People with COVID-19, which is the disease caused by the coronavirus, spread viral particles through coughing and sneezing. The particles can land in the mouths or noses of those nearby.
It might also be possible to catch SARS-CoV-2 by touching a surface where the virus has recently landed and then touching one's mouth, nose or eyes, but CDC officials believe this method of transmission is less common."
