I was thinking for the reviewer. Also note that I was only answering as to why it wasn’t done in the past.
For the time comparison, I’m not sure, it doesn’t seem quite apples-to-apples:
1) It is scheduled time vs unscheduled.
2) There must be some base rate consideration… the papers being discussed here were planned to be desk-rejected.
Maybe it could be a good process for saving papers that were going to be desk-rejected, but I dunno, that seems like it’d just lower the quality standards.
But it's not the reviewers who do it, it's the handling editor. Who spends relatively little time per paper (compared to authors and reviewers).
Honestly, I was sloppily thinking of the general reviewer/editor system as one thing (and didn’t notice that I’d lumped them together until you brought it up here). Good point. Although the editor has a lot more papers to handle, so I think they are probably busy as well.