I just mean that there's nothing inherently sincere about plainness and simplicity. Some people adopt a plain and simple style disingenuously, and others write in a more flowery style out of a genuine aesthetic motive. In French, 100 years ago, the kind of style you're advocating would have been the "marked" case. That is, readers would probably have attributed disingenuous motives to someone who chose to write a history book in the style of spoken conversation.

>Plainness, simplicity, straightforwardness are words that would describe "as spoken" writing. They are also literally antonyms of "affect" in this context, which would mean pretentiousness, artificiality, pomposity.

"Spoken writing" can be just as artificial and pretentious -- e.g. upper class writers writing as if they grew up in da hood. Or people dumbing down their language to sell more.

How we speak with a friend, and how we write, doesn't have to share the same language or tone or expressions or vocabulary even. Spoken is a stream of consciousness that we express in real time. Written is forever, so we have time to refine what we write, go deeper, be more artistic, add flourishes, and so on. This is not the same as "being obscure for being obscure's sake".

To make an analogy, what you ask for, in photography terms would be "all photography should be real life documentary-style scenes".

In fact, even "spoken" changes form all the time: you don't talk to your bong buddy the same as you talk to your parents, or spouse, or the same way you give a lecture as when you casual chat over coffee, or when you teach students. Tone changes, expression changes, vocabulary changes, level of difficulty changes, etc.