Active users per day seem to have doubled since June, but that was the peak for posts and comments. While top level comments (ie. posts) haven't much dropped, reply comments have dropped by about a third since that peak.
Increasing daily active users while comments decrease seems to imply an increased prevalence of bot voting.
Hmm... Perhaps everyone is too busy posting to reply to anything... Pretty typical in life, too. Folks would rather talk than listen.
Why would that pattern of general human behavior change over the course of two months?