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.

Another question is: why would you need it for a key?

Long-established public/private keys and signatures are used in this way all the time to control access to servers around the world. No blockchain needed. Blockchain is helpful when we all need to agree on a series of events.

Homes are a nice example of where you can have an isolated system which knows what it needs to about you (e.g. a public key) without sharing or cross-checking anything with the world.