It's hard to write without a specific audience in mind, or without social feedback. This is true but backwards. It's more natural to say that we want to write when we want to be understood and feel that writing would be an effective way to achieve that.
The same is true of other forms of art.
Writing as extended memory
Early forms of writing may were for recordkeeping, and writing has always retained something of the character of a permanent artifact - a drug that counterfeits memory, as Socrates says in the Phaedrus. When I am motivated by this aspect of writing, it's because I'm experiencing a shortage of working memory and mental swap space, so I extend my mind onto some other medium via text
The motive to extend my mind precedes the intent to write something down. If I'm not motivated to extend my mind, it's not that I can't do this sort of writing - it's that it would be an absurd farce to pretend to try when I don't in fact want to.
Writing as imitated speech
Speech has a different history than writing, almost certainly originating as social vocalizations of some sort that communicate the sorts of things nonrational animals want to communicate. Normal monkey stuff, in our case. But by the time alphabets were invented - and perhaps to some extent earlier - we've written in order to create durable, transferable, unchanging records of speech, overcoming the ephemerality of what Homer describes as έπεα πτερόεντα, "winged words."
We vocalize a lot more than monkey feelings, and I'm mainly concerned with descriptive speech here, as that's what people say is hard to write down. Speech is a social act - it's for others to understand and respond to. We're social animals, and we simply don't want to speak to nonspecific people. This isn't a defect in a system designed to produce output on demand, like GPT-3. Rather, humans have specific capacities and motives, that are responsive to the circumstances in which we find ourselves.
Writing from specific motivations
Excerpts from a larger discussion about simulacra came from an email chain in which I was building shared models with friends, a combination of the extended-memory and imitated-speech motives. I've also found myself motivated to engage in dialogue on Twitter, because I'm in actual dialogue with others, not talking into the void, which is not a thing a happy monkey does very often. But I want artifacts to point to sometimes, so I'm going to see whether I can convert some of my more interesting Twitter threads into articles.
This essay started as a memory of a point I remember making a couple times in person, that therefore seemed worth creating an artifact of, an imitation of speech - but then in the process of creating an artifact, I added some detail to the model, which is more in the mode of writing as accounting.