https://theconversation.com/why-does...20mass%20media.
I think we are both obviously hobby scholars. I have no academic training in this field.
So I remembered that Google is my friend and found this article. It basically backs up my theory. I swear I didn't read it when I first wrote what I did. I just basically based what I wrote on everything I read and learned in the past.
Your theory is also a valid point. And I don't know about Australia, but there are many accents in America, if not what you would technically call a dialect. But you are forgetting that when those 2 countries were formed, literacy was already wide spread.
Most of the first settlers in America were basically from the same community.
This is especially true of the Pilgrims of Plymouth colony, if not so much of the Jamestown settlement. As a matter of fact, the Plymouth colony might have been the first settlement in world history where every resident was literate.
The Puritans made sure that every man woman and child could read and write so that they could read and study the bible.
Edit: regional dialects are common in all of Europe, not just Britain.