There's more to it. A TPM comes with an endorsement key certificate, and the platform to which the TPM is attached can come with platform certificates, and the

There's more to it. A TPM comes with an endorsement key certificate, and the platform to which the TPM is attached can come with platform certificates, and the OS can require those to exist and be valid and that the TPM still have the corresponding private keys. An OS can use those keys and certificates to implement a garden walled by secured boot + attestation. The user gets to change the relevant key hierarchy seeds, thus causing those private keys to no longer be available, and those certificates to be useless, and the OS to no longer be able to do attestation using those keys and certificates -- but then the OS vendor gets to lock that device out of the walled garden.