When you exhale, you do not exhale pure individual virus. You exhale relatively large droplets that can contain the virus and any other stuff. Yes the virus itself is way tinier than the holes in the weave, but you are actually exhaling droplets of water (all the time when you talk, cough, sneeze etc), and it is those droplets that are large enough so that they are caught in the fabric.
Masks protect others from your exhaled germs.... Surgeons have been wearing cloth surgical masks long before the n95 existed for this very reason.
I don't get the reasoning that if something is not 100% then what is the point... my seatbelt or carseat is not a 100% guarantee against injury in a car accident, but no way am I driving without them...
nice article from John's Hopkins
https://www.hopkinsmedicine.org/hea.../coronavirus-face-masks-what-you-need-to-know