Because the metadata is authoritative as signed by the npub.
Discussion
That’s how you find out the nip05 which is then can be cross-validated.
thats true of every kind.
but in this case can be instantly replaced and have different values on different relays.
so you also need to factor which relay you are using as source of truth like you do root dns
Maybe we need to spec a 'home relay' in the kind 0 event where the latest should be found.