Great question! Relays aren't involved in curation or discovery, so it fall on the client.
You can request very broad subscriptions from relays! For example, here is a site that subscribes to everything, showing you a gods-eye view of events streaming into a relay:
I doubt anyone has ever been successful into signing up on any social platform and just followed the big names that are suggested automatically at the beginning or based on some "key interests" you select.
But hey, if you want that, it's easy for a third-party website to grab a ton of public Nostr data and build custom recommendation lists and whatnot.
