Maybe I’m a weirdo but I tend to look at peoples mouths more than their eyes. I’m not hard of hearing, but I feel like it helps me follow conversations better.
Even today, this is still pretty common at cashiers and checkouts in Canada, for example.
Many of these barriers were put up rapidly without much thought, and are completely improvised. They aren't like the purpose-build security shields that still have holes, vents, or microphones/speakers to allow at least some verbal communication to take place.
The thick, rigid plastic barriers are the worst offenders, by far, although even flexible plastic sheets can definitely disrupt communication, too.
Different individuals submit to varying degrees, and in different ways.
Some people become very quiet and withdrawn, which can lead to the problems you describe when they try to communicate verbally while masked.
Others feel intense paranoia, and desperately seek out authority figures to latch onto.
Yet others realize that they're submitting, and it makes them feel weak and powerless. These are the individuals who often react aggressively when encountering somebody who isn't submitting like they are.
It's quite a fascinating subject.
Like you just described, somebody else wearing a mask can impose a significant accessibility burden, even for people who may not necessarily have hearing difficulties, for example.
Encouraging, or even forcing in many places, people to wear masks was truly an accessibility tragedy. It's made even worse by the fact that widespread everyday masking isn't even effective. A lot of people were forced to endure a lot of unnecessary and unjustifiable suffering.
Same.
I’ve done this since I was a child.
A side benefit is that I have become half way decent at reading lips.
I learned at some point (teens?) to look at my conversation partner’s eyes in certain situations, but it’s not my default.