How do you enforce contracts all around the world without having to hire lawyers from all jurisdictions and hope for timely legal resolution on any jurisdictions?
How is a NFT enforceable in contrast? There's no way to prove who owns what address, e-contract, etc, that doesn't just fall back onto standard established contract law.
If I sell it, the NFT isn't going to notice that it is on display in a museum and take appropriate action.
And so on. Smart contracts are neat, but they depend on all the same mechanisms that other contracts use.