I think this is a good analogue. A smart card is a challenge-response system where sure you could extract the inner key, but doing so would take time and require destroying the card, which would alert the user— we all learned years ago about skimming and now the payment terminal comes to our table rather than the card being carried off elsewhere.

TPM is one piece of a larger puzzle and provides a middle ground where among other things you can get full disk encryption without needing to input a memorized key on every boot.