It’s not rocket science. The mask wearers cannot breathe through the fabric alone. So they inhale a mixture of stale air inside the mask and air sucked in from around the edges of the far-from-airtight sides of the mask. They then exhale the air, part of which stays inside the mask and the remainder of which is exhaled out the sides of the mask. Not much protection from this, unless the wearer is a sneezer. The wearers also have to breathe more to adjust for the oxygen deficit, which increases the exchange of any germs. But the masks make people feel safe and virtuous, so we are all forced to wear them.
If you can find an N100 or N95 with exhaust valve, then you won’t have that problem or have the glasses fog up. I still pull mine up for a breath every 10 min or so ...