Sure there's an element of that, but for some people it seems much worse than others. Some people can still speak clearly with a mask on, but many people can't.
It can be particularly bad when there is a plastic barrier of some sort in front of the masked speaker.
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.
