If you turn on show dead, you'll see that some accounts just post spam or weird BS that ends up instantly dead. I think Evon LaTrail is gone now, but for years posted one or more links to his/her/their YouTube videos about personal sanitation and abortion per day.
There is a stream of clueless folks, but there are also hardcore psychos like LaTrail. The Svelte magazine spammer fits in this category.
I've definitely seen comments that feel very authentically posted (not LLM generated) but are a weird mixture of vitriol and spite, and when you list other comments from that user it's 90% marked dead.
I often wonder if the user is even aware that they're just screaming into the void.