Why couldn't they have put the key in user-resettable memory which erases the disk encryption key when cleared, like with TPMs for example? It was a poor design to even allow it to be used this way.
If you care about this specific attack scenario then make sure you check the keys with a management tool or something. It's not necessary to make the chip unusable for almost every aftermarket user just to make it a little bit clearer that a compromise has happened in that rare case.
I'm just trying to speculate what might be driving demand for this type of feature, since TPMs already exist.