This is the reason:
Looks like the PieFed’s old post deletion does not take into account whether a poster is local to a deleting instance or external to it.
At least one banger of mine on this comm is already affected.
Memes on piefed.zip should be safe.
Even though you might post into a Lemmy community, piefed.social still has to store the original copy of the meme.
It would be good if the instance chooser showed content retention policies in some way so people could take that into account when they choose an instance.