Deleted my comment because you said it better.

And an addendum to this behavior, dunno how aggressive Piefed and Lemmy are for pulling information, but I've noticed interactions keep making posts and the skeleton of the community propagate/federate.

And though the search function can't pull posts from when the instance was active, it can pull comments to those posts and that are from still active instances, which then pulls a skeleton of the post and of the community.

And though rarer, in fediverse softwares that allow following, doing so to someone that interacts with older posts also helps pulling these derelict posts.