I think for the same reason that you might hang out and converse with people. I've unfollowed a lot of people, so my feed has been pruned down to mostly interesting content. I occasionally post something that I think is interesting, relevant, and not widely known. Of course, there's a performative element, but that's true of all social interaction.

I mean, I get that a lot of social media content is narcissistic and vapid, but it's tool that you choose how to use.