If the mask stops some droplets (which it obviously does, as it gets wet over time) and some of those droplets carry the virus, then obviously the mask protects against the virus - not 100%, but some percent (just like condoms!).
I'm thinking that for each virus there is a chance that it will infect a cell. The higher the viral load, the higher the number of chances that you will get infected.
a lower number of droplets -> lower viral load -> less chance to be infected.