I find it a bit hard to follow the argument at times. Textbooks as tools for auto-didacts go back a long way, and have accomplished some remarkable things. Luca Pacioli’s 15th century textbooks on accounting are credited with making the entire Renaissance possible, due to the dissemination of the double-entry method. He didn’t invent the method, but he was the first to explain well in text. Copernicus’s treatise on the motion of the planets showed the possibility texts, and changed the world as well, as one of the early triumphs of print.
What they both share — their content-ness, as it were — is an understanding that they must make themselves accessible to a wide variety of contexts. The reader’s context is not the same as the speaker’s context, so a new sort of prose must be made which takes this into account.
I’m not sure that’s the same as “dumb this down so anyone gets it” — it’s more a way of saying “You don’t have followed the conversation up to now to understand what I’m about to write”. It strikes me (or has struck me previously, I suppose) that this is a form of hospitality to strangers (a term I’ve probably bastardized from Derrida and Kate Bowles) and is largely a good activity, when balanced with other activities, to engage in. What am I missing?