I always figured one of the effects of a mask was to prevent spittle and sputum from ordinary speaking from getting around. Either to within the mask from without or vice-versa.
A particle of spittle due from pronouncing a fricative gets out, floats around, the moisture evaporates, and the bugs it contained float around for even longer and for a greater distance.
Sort of like salt air spray from the ocean, where the water evaporates, and the micro-micro particles of salt still float around for quite a distance inland.
Masks also tend to keep you from rubbing or touching your mouth and nose, which is a known transmission vector for nasties.
In my opinon (no science involved) the slight moisturizing from your breath helps to trap the actual germs, and I suspect if the "underwear experiment" were performed with even a very very slight dampness, the results would be much less than dramatized in the OP.
After all, analogously, they treat regular filters (as on your intake manifold or your furnace) with resins to help trap nasty particles from entering your engine or getting into your house.
Ninety percent isn't as good as 100% but it's still better than 80%.
Honestly, this silly actively looking for negatives about the masks is ridiculous, and if people think it is for control/training purposes, I don't know what to think of y'all. Bunch of "Typhoid Maries," as far as I can tell.
There. I said it and I ain't takin' it back.
In fact, I've said it before.
Terry, 230RN