People tend to forget that all those memes and videos need space and those media files are replicated throughout the network and depending on the media caching policies on federated instances, this takes as much space as on a local storage.
and to add something here. I think that the resources compute/memory/storage/hardware needed per user on the fediverse are much higher than on a centralized platform like twitter.
@dichotomiker@qoto.org Most storage backends have that feature, and I would be astounded if Twitter would not use that. If not on the storage backend, then on some other infrastructure layer, since pictures and videos are a use case which is undoubtedly a scenario in which deduplication works well.