The guidance from the highest levels of the scientific community has been abundantly clear for months now - wear a face covering in any public indoor space and when you can not maintain social distancing in an outdoor setting.
The reason we should all wear face coverings in public is quite simple: face coverings help prevent you from spreading your germs to others and help others from spreading their germs to you.
Airborne particles spread "mainly from person to person, mainly through respiratory droplets produced when an infected person coughs, sneezes, or talks. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. Spread is more likely when people are in close contact with one another (within about 6 feet).?" It can also spread by pre-symptomatic and asymptomatic individuals, so wearing a cloth covering in public, even if you feel perfectly fine, can help protect others as well as yourself.
As this CDC drawing shows, wearing a face covering helps prevent particles from freely spreading when you talk or cough.
The CDC and Surgeon General Jerome Adams have also released a video which teaches us how to make a face covering out of items we can all find in our home:
Certainly makes sense. The CDC didn't do themselves any favors lying to the American public for the first few weeks of the outbreak though, so I can at least understand the confusion and mistrust some have with the CDC on this.
That said, the messaging has been on point and logically obvious for months now, like you said. For a while it wasn't easy for everyone to buy masks online and it took a while for everyone to understand how easy it is to make a face covering at home.
But at this point there is little excuse to not have one and wear it when you can't socially distance responsibly. Its the only tool we have against the spread, so its a solid compromise to 100% quarantine lock down measures.