'Cause sometimes you're all "man I wanna thread about armadillos or some shit" and it's nice to think about, but then you realize that a thread about armadillos might be awesome 'cause, you know, armadillos!
Or maybe it's just a thread that after you start it you realize that it's just positively crawling with poo bugs, and no one wants to touch a thread filled with poo bugs.