Blockchains are a poor database for social media. They are extremely slow, overly complicated. And it’s Just a immutable data structure. That’s really why every attempt to use one for anything but currency has failed.

They don’t really offer anything a Nostr relay doesn’t either.

Both of them work off private keys to verify ownership.

Both of them are decentralized. But Blockchain sizes are huge. Each node is terribytes in size

Unlike block chains, nostr is super easy to develop for and can scale very well.

You could make it more decentralized by adding in some peer to peer tech. But even torrents need trackers. Which is basically a relay.