What I'm wondering is if the efficiency of the spider itself has dropped. I've often hunted for an old Reddit post I once saw a long time ago and found no hits - maybe I got the wording wrong, but I suspect the real reason is that lower-popularity reddit content is simply not getting indexed at all. Or maybe it's the extreme recency bias others have discussed. Of course, I have no evidence because I can't find the thing that I can't find.