“If they prevent an infected person from releasing viruses, why would they not prevent an uninfected person from taking in those viruses? “
The viral load in the air is very small so generally there is no virus to take in.
If you must maintain close contact with an infected person then you should were a qualified mask.
The surgeon doesn’t were the surgical mask for his protection, he wears it to protect his patient.
When I go to the store I wear a mask because it makes those around me feel better.