The American Revolution was spread through pamphlets passed out at the local tavern. Newspapers played a major role in educating the people about the Revolution and passing around the text of the Declaration of Independence, Articles of Confederation, and Constitution, so no, it was not reasonable for some people not to learn to read 200 years ago.
By the way, if Gutenberg's Printing Revolution made the written word so cheap that pamphlets could be handed out to as many people as possible, I don't think there would have been many who could not afford books 200 years ago. If there were many who didn't use the reading skill much, then there wouldn't have been all the hoopla over the Stamp Act the British imposed on the American colonies. You sorta need to know how to read to make any use of stamps 200 years ago.
I think it was reasonable for some people not to learn to read 200 years ago.