They share them as a once off. Very occasionally you'll get the "Update: MIL stole our baby" posts, but mostly it doesn't matter (and shouldn't matter) who is posting the content. In social media, who is posting matters.
You have the oddities on Reddit occasion like that terrible poet and the comic lady that has her OF simps brigade her posts, but just look at how utterly useless and rejected all of Reddit's attempts to turn it into social media are: follows, journals, chat - features of genuine social media but done poorly and with the wrong audience who distinctly Don't want to follow personalities.