That isn’t required for a key. What if I want to let my family member access the house tomorrow while I’m out? Do I have to sell it to them?

The key/lock relationship is not connected to ownership. Ownership could be connected to the ability to issue new keys, but even then the ownership doesn’t need to be logged in a blockchain for that - it can simply be signed by a key held by the land registry.

If you want to make an argument for using blockchains for the land registry then… go ahead, but it’s another discussion with a whole different set of arguments.