TL;DR: peer-review times appear to have been growing for a long time. The effects of COVID-lockdowns on peer-review are surprising.
A few months ago, I was invited to referee a research paper. So, I guess the editor thought that I was one of the 2 best people in the entire world to review this thing. That’s how it works, right?
A few days before the deadline (and after expending considerable time on the task), I received another email from the editor which I opened excitedly. The email said that he had now received THREE referee reports on the manuscript and no longer needed mine…
So, in this case, there must have been at least 4 referees (including me) considering the manuscript at the same time. (It’s anyone’s guess how many invitations were sent out.)
It’s obvious that journals can reduce processing times by inviting more reviewers than they need. But you only need to think about the consequences of doing this to see that it leads to rapid exhaustion of the journal’s referee pool and, therefore, causes longer processing times on average. Referee time is a finite resource!