If you want to understand why masks may not work to slow transmission, look at this diagram. Now a lot of virus is in droplet size that will get trapped, but what happens to those once trapped? They sit on the mask and eventually get broken up into smaller particles which can be pushed or pulled through the mask, much less slide around gaps in mask fit. Particles sitting on or in masks are also subject to touching. Now imagine what happens as you wear them several hours a day. And remember the study finding that the virus survives for a very long time on medical masks.