There’s also the fact that instances can simply choose to ignore delete requests. Because that’s all it is; A request. Let’s say I post on .world and it gets federated to other instances. If I then delete that .world post, there’s nothing requiring those other instances to actually delete anything. .world simply sends a delete request, but the individual instances can choose to ignore it if they want.

That’s a large part of why the “I delete my content after a day or two so LLMs can’t use my data” crowd is so stupid. If someone was looking to train an LLM on Lemmy data, they’d simply set up an instance to aggregate posts, and refuse to delete anything.