You don't wear a body armor thinking that it'll save you from 100 AKs, you wear it hoping that it might help your chances against a stray bullet.

Similarly, you don't wear a cloth mask to enter a ward of 100 covid patients all coughing at you. It would be almost useless in that case. But it can help if you're in a store where one of the customer is infected and might breathe in your general vicinity.