I think, if you look at the list, these are just the people who post the most. So it’s fairly coincidental that they also have the last post in a given thread.

Just because someone has the last word doesn’t mean they necessarily “killed” the thread; in a sense, I think most threads die of natural causes, and somebody has to be last. Not to mention necro bumps to threads nobody is interested in anymore – those were more “killed” by the person before them a long time ago.