The primary purpose of Bitlocker (when used with a PIN + TPM) is it makes a powered off computer or a drive itself as good as a brick. Assuming the TPM doesn't

The primary purpose of Bitlocker (when used with a PIN + TPM) is it makes a powered off computer or a drive itself as good as a brick. Assuming the TPM doesn't have any key extraction vulnerabilities. Keyword is powered off. With any general purpose drive encryption, the TPM doesn't actually decrypt the bulk of the data as its too slow so the OS eventually ends up with a key that is extractable.