You mean NIP-05? The bots I see are all domain verified. It just doesn't impose the kind of cost that stops them. By requiring an on chain address with funds it means that the spammers at least have to lock up some amount of Bitcoin. It doesn't introduce a scaling cost per identity so maybe not that helpful. But perhaps the flow is instead having an address created by the Nostr identity being "verified" or "vetted" that must hold some arbitrary amount of Bitcoin.