Caching an ever growing pool of data indefinitely quickly becomes a significant maintenance cost for relays as Nostr scales. Many relays may decide to prune data after certain intervals. Others may offer to ensure the maintenance of your data over defined periods of time as a service. Our you can run your own sovereign server and just backup all your own stuff for like family posterity I guess.

That makes total sense. I may need to run my own relay for that purpose.