Even if you don't know anyone, you can run a local network in your town, and it only takes one node to find a node from the mainline big network, for everyone to be entangled in one big network... tell me this is not different from how nostr clients discover relays :)
Come on man, yes Nostr can become a DHT, a small one, but it isn't, not even close, it is not behaving that way and paid relays (the only sustainable ones) have no (almost negative) incentive in losing their advantage as the scarce common well known relays