DNS needs to resolve an name on the order of nanoseconds across a distributed system. It is designed with this in mind. A blockchain is designed with integrity in mind. Wallets can verify transactions on the order of nanoseconds with SPV--also distributed because a client can get the intermediate block headers from any server. Querying data, like for DNS, has constraints different from verifying integrity, like for a ledger.
Sure, you can use a blockchain for storage, but who do you trust to do the lookups? It can't be on chain because it will be far too slow. You'd end up having to trust some entity like Cloudflare to run a DNS-on-blockchain node that stores the ground truth, going full circle back to regular DNS. What's the equivalent of SPV for DNS-on-blockchain where I can do and verify name resolution with limited resources?