Someone said itt that they don't confer ownership but that's not accurate. Contract law doesn't care if your agreement is written on a napkin or a dream, as long as it happened
Think about it this way. If I own something, and there's not a requirement in law to use a certain kind of ledger, such as the various title systems in place for recording land ownership, I can transfer ownership however I want. Like you said, contract law doesn't care where the agreement happens.
So even if NFTs really conferred ownership in some sense, I could buy ownership of something via NFT, then turn around and sell those rights myself outside of the blockchain. I could just draw up a contract with quill pen and parchment to seal the deal between me and the new buyer.
Now we have a new owner of the thing that used to be an NFT, and we have a token on the blockchain that is meaningless and doesn't correspond to the ownership of anything. But there's no requirement for me to publicize that fact, my off-chain sale won't be reflected in the blockchain. I could even go on and resell the token, pretending it's still valid, and no one would be the wiser. At which point you have to ask: if NFT tokens may or may not represent ownership, and there's no way to tell if they do, what was the point of all this? What did we gain over parchment?
The imaginary property system people
think they're using when they do an NFT is more like
entailment, which was abolished a century ago. Under our current legal system, you can't say "I sell this to X, but only on the condition that he never separates ownership of the object from possession of the private key for the corresponding blockchain token, and imposes this same condition on any future buyer".