The entire point of an NFT is to act as a sort of proof/certificate that this is the Real Version of a given piece of media. Someone could create a new NFT on a

The entire point of an NFT is to act as a sort of proof/certificate that this is the Real Version of a given piece of media. Someone could create a new NFT on a different blockchain for the nyan cat, but it wouldn't be Your NFT. As a result, it could be said it's not the Real NFT, and thus doesn't have the same value. An artist selling their art as an NFT would probably say "hey This NFT on this chain is the real NFT for my art, anything else is a fake". A fake would never have this announcement, and there wouldn't be a record of the original artist owning/creating the NFT on the new chain. So it's not so much that one blockchain is the defacto NFT implementation, but it's up to the creator to specify the blockchain that has the defacto NFT for that piece of media. They could even announce their own signature, and point out the transaction by their signature that created the NFT. Or something along those lines