In the month of October, the news is full of stories about ghosts and other mysterious subjects, so people are more drawn to groups like this, but once Halloween is over, there are hardly any reports in the news for a while. So maybe it's an out of sight, out of mind, sort of thing.
I think that there's such a big build up to Halloween in groups like this one that once it's over, people just sort of take a break. Kind of like with Christmas. People are all excited waiting for Christmas Day and then it's over in a few hours and they feel a little down and need a little time to recover.