It's because /hs/ users used to use the chat a lot but it's dead now so they make threads to use as a chat.

Although there is legitimately a schizo mexican faggot who uses proxies and only spams shitpost threads with tiktok videos of trannies and that guy is annoying. Fucks up the board's quality a lot because he doesn't get contained to a single thread and feels the need to post his shit everywhere like a kid, at least the in the other case the shitpost behavior doesn't leave out of chat threads.