But that's just a private journal that could be a text file somewhere. People have been doing that for centuries without publishing it. If anything, it seems clear -- given natural human tendencies -- that an actually private journal that you don't think will be published seems more valuable.

It's not the same. There must be an affirming feeling to putting your thoughts out there and not getting pushback on it, you feel more confident in yourself. You could imagine what good things come from confidence

Same for me, I write to get my concepts and ideas ordered and polished. I think it is important to communicate with the public, even if you get no responses. 99% of users only read, 1% reply - still, you have an impact on both groups. Confirmation is really not necessary (and confirmation may also have a negative influence on behavior and incentives, see how Instagram affects motivations to share pictures).