My previous laptop got struck by lightning last month. Because I had a passphrase & not TPM for unlocking, I stripped the NVMe from the board, put it in an enclosure, entered the passphrase, & now I can access all my data for recovering from that situation. Had I tied it to TPM, I wouldn’t be able to recover my data (ZFS & Bcachefs only have one ‘slot’ for passphrases so no secondary, backup key)—while, as you pointed out, a thief can just boot the laptop they stole to get the data. Point being: passphrases offer advantages while being dead simple.