It is about full disk encryption with automatic unlock during boot. One needs to make TPM dependent on a successful secure boot to allow access to decryption. The boot completes no problem, but the TPM entry that controls access needs to be manually recreated with each new kernel update.
To defend against an attacker with physical access to an offline machine you need to verify anything that the attacker can overwrite without the encryption key. Aren't bootloader and kernel on the writable unencrypted partition?
The signature that's validated by secure boot. If you don't have secure boot turned on then there's no point in verifying PCR 7, because all PCR 7 contains is the secure boot data.
See https://gist.github.com/jdoss/777e8b52c8d88eb87467935769c98a... , the bit "then auto volume decryption on your next reboot will fail". This makes sense.