it's like an emergency stop button: you ideally want it as close to the "start" button as possible.
the worst time to make a user go hunting for the "hide this" button is immediately after they've had to click a button to show it and been hit with something they don't want to see.
(mastodon's "show more/less" text changes the width of the button as well, and that can end up making the button move since it might (not) fit on the current line.)
(edit: the cohost one is particularly egregious because the buttons could just be in the top bar. it's not like it goes away when you show the content!)
