I also think a big part of it is how active users are counted. Saw in a different thread that it only counts accounts who have commented or posted in the last month. Well… I browse and vote on probably an average of 30-50 posts and many of their comments every single day, but the last comment I left was over a month ago.
I also wonder if the active user count is counting people who made multiple accounts across different instances and was therefore always massively overinflated to begin with. I have 5 lemmy accounts - one on lemmy.world when I first joined, one on lemmynsfw for happy fun times, and 3 more trying to find a different instance with the de federation policy and hoster that I wanted after lemmy.world was going through their ddos downtime issue.
Did they stutter?