Hiemere3
My hypothesis? The numbers are down. These people are not coming in to the JW religion anymore. Kingdom Halls are filled with 2nd and 3rd generations of born-ins who don't know of anything else. Those who started the stories either left, died, or are too old and have stopped passing them on. No new people from the general public, no new ghost stories. No ghost stories, then no "demons," because to Witnesses all ghosts are "demons."
Interesting and well thought out reply.
In addition, OrphanCrow is correct when she says that this was being promoted from the leadership through print.
Could it be like the stories of folks being kidnapped by aliens (which are also decreasing) that have severely dropped now that there are cell phones that could actually record the event?