To me, it is a feature to have a password required at boot to unlock the drive. Relying on TPM for keymatter is convenient but comes with caveats I don't like. I don't personally trust that the boot chain and OS on a modern system are secure enough for this model to be similarly secure to using a passphrase properly. And if I care enough to try to secure something in this way, I definitely care enough to pick something that I believe would be at least truly secure at rest with a decent degree of certainty.

TPM based unlock does at least still fulfill the goal of ensuring data stored to disk is encrypted so that it can't easily be recovered from a discarded drive.