It’s a really important point that different people use social media differently and expect different things out of social media.
The reason I think this point is so important is because too often users will think the system works one way and expect it to work that way when in reality it’s working a different way.
That applies here. You bring up the idea that most of what we do on social media is targeted toward the public, and platforms like Twitter and Mastodon seem very focused on that mode, and there’s absolutely nothing wrong with that.
However, a user that expects more privacy and less targeting toward the public might find themself surprised if their content is much more public than they were expecting.
So that’s why I grind that ax pretty regularly.