I write mostly for myself. That's a trite I guess observation considering that I happen to write a lot of private notes. But I think writing for broadcasting is overrated.
Journaling or diarying is writing for myself, and often in a form that will never leave the disk inside the the computer. But I also want to write more complicated things than just what I thought about today, how I solved some problem, or a reminder for three months from now. Why? Because writing as a solitary pursuit is similarily rewarding like reading for pleasure. We can read without growing an audience. We can read without have any extrinsic motivation. We can just do it and leave it at that. But writing is a bit too much associated with communicating (small) and broadcasting (large).
I could probably write a book on the most idiosyncratic topics, something that not even my mother would like to skim the foreword of. Because imagine if that process would help me know myself? How valuable would that be? The writing artifact might be useless, even. But the process could be enriching.
I would never hope to read a book by someone I don't know and be able to absorb their wisdom, not even 10%. Some things cannot be transmitted like that. The printing press probably has not helped us know ourselves more than just, you know modestly more. Some things have to be worked on by you and you alone.
This also translates to more practical subjects than knowing yourself. But that's what I felt like spending the word count here on.
But in terms of public writing. I am currently working on an article-length piece for a niche "publishing". And I find that process to be rewarding.