I remember people using tools such as Greasemonkey to redact comments on Reddit using scripts to mass-replace the content of their comments with babble. If comments don’t get truly deleted when they are deleted or can be brought back up in some way, then editing comments to replace the content of them with babble is better. That’s my two coins anyway. I think something similar is happening here. Another factor could be that some instances might not federate comment deletions as well as they do with edits