A lot of people want a more physically certain level of data destruction than such a command provides. If I saw that a drive wrote 3-5 passed of junk data before zeroing the disk then I would trust it but such firmware level info is rare to impossible up find.
Since when there is private key in AES? And that requires a paranoid person to trust that a company does not holds the keys in escrows somewhere or are by any way retrievable.
