That’s one of the use cases NFTs were meant for, noncustodial transferable digital property.

How would you: make the key transferable and secret, while still notifying the original vender it happened, and collect payment, and keep me from selling and turning off the key?

And once the vendor went away, no new keys would be issued. So why make a public crypto ledger, when their ledger suffices?

Just like an NFT. Useless in this case too.