Your faulty assumption is that social media is someone's only input. Why can't I have a nice little oasis to chill at between battles for my right to live?
Shallow exposure to other experiences never told me much. People hold back out of fear of harassment in a place as public and algorithmically tuned toward creating negative experiences as Twitter. Mastodon and the fediverse improve on that slightly by not having the algorithm, but there's still harassment.
I certainly don't reveal my whole self on social media. I open up a bit more in places with good moderation like this, or places where I control the comments like my blog.