@darius I suspect there is a bit of "instance churn" that contributes to this as well...
By that I mean new people who signed up for a big/general-purpose/well-publicized instance find it too slow, or has the wrong vibe or whatever decide to move instances (maybe the smaller surge back in April are now moving over during this surge? Or jsut new people instance-hopping?).
I know that instance moves can cause a brief blast of ActivityPub transactions and thus sidekiq jobs, and perhaps there are enough happening out there to make a significant contribution.