A lot of them are edgy underage children and don't know any better. They think that they have a dark sense of humor but really they've lived a life disconnected from those words, so they like the idea of pushing others buttons at no cost to their selfish existence.
not only attention seeking, sometimes the motivation is "to spread the truth", at least as they perceive it, and sometimes it's people who get triggered and are not able to stop their rants