Why do you presume that it should be easy enough for them to use without training? Keyboards are a pretty simple technology, and serve as a subset of the primary interface to most modern AI models, but training is still required to use them well. A user who's never learned proper keyboard skills will type much more slowly and with much more frustration than you or I can, and that will have meaningful impacts on their ability to perform tasks requiring a keyboard.

It's just a kind of training that's receded into the background as "normal", and that many of us who enjoy recreationally typing out comments on the Internet self-taught.