The masks people are wearing will not protect anyone from the virus. The virus can go through them. Imagine wearing them for a long time how filthy those masks really are.
The virus doesn’t float in the air by itself, it’s suspended in tiny water droplets. Wearing a proper mask significantly reduces both the chance of breathing those droplets, and the chance of spreading them to others.
Why is that hard for you to understand?
Viral particles often ride on water droplets (like from a cough), and a mask *can* stop those. Focusing on just the size of the actual virus is not helpful.