Relay lists should be distributed to as many relays as possible by clients. There are also some aggregators that crawl the network for those events and store them (purplepag.es, profiles.nos.social and nostr.band), if they don't have the relay list is likely because a user hasn't published any.
> Why do you think they should create one?
To make the outbox model work in practice we need people to have relay lists.