Maybe some bigger subreddits are dying, but the UFOs and Experiencers subreddits are as active as ever, if not more. I guess these remain big there because these subjects are very censored in other social media (e.g. youtube) and never show up in search results (they show only videos from tv news). Reddit also censors them (e.g. some posts that contain more info than usual), but you can still see these posts when you go to these subreddits directly.