It’s not and never claimed to be. Lemmy is a piece of software, the instance owners and community moderators choose what stays and what’s goes, every Lemmy instance is just a glorified forum of old internet. Federation means the post isn’t solely controlled by the instance owners, but deletion is federated so the instance deleting it sends notice to every other instance where it exists to delete it as well, and then it’s up to that instance to do it (tho Lemmy will do this automatically so it would require altering the server code to stop that)