Hey brother and good morning. 2 things:
1. It's unhealthy to breathe through the same mask continually. The mask itself will acquire germs over time. As well, breathing through masks allows less oxygen in and less CO2 out so the quality of the air getting to the bodies cells is reduced. This is not exactly conducive to a learning environment. If you recall, the whole idea behind school breakfast and lunch programs was that children needed the proper nutrition to be able to learn optimally.
2. Children learn speech correctly as the watch the mouths of those speaking move as they ennunciate words. This, of course, was widely restricted by masks.