>Unless the disk supports RZAT, the only way you can guarantee that the disk won't return old data in response to a read command is to write zeroes over that block.
While this is true (the disk will never respond with old data once you have zeroed it out) it is important to remember that even zeroizing the disk yourself isn't a guarantee that the old data is actually gone from the disk itself - the disk may present itself as a raw block device, but internally it may use error correction, write amplification prevention, or error prevention schemes which may mean that old data will remain on the disk even though you have written zeroes over it. For example hard disks remapping bad sectors, or SSDs relocating chunks of data when the EEPROM gates in that chunk are starting to wear out. You would have to use forensic means to recover this information but it still remains. The only way to guarantee that the information cannot remain on the disk is to use encryption and make sure that the unencrypted key never touches the disk.
I don't think people care about the idea that a sufficiently advanced attacker with physical access the hardware can restore old data anywhere near as much as they care that the next customer along gets a fully readable copy of your data just handed to them.
While this is true (the disk will never respond with old data once you have zeroed it out) it is important to remember that even zeroizing the disk yourself isn't a guarantee that the old data is actually gone from the disk itself - the disk may present itself as a raw block device, but internally it may use error correction, write amplification prevention, or error prevention schemes which may mean that old data will remain on the disk even though you have written zeroes over it. For example hard disks remapping bad sectors, or SSDs relocating chunks of data when the EEPROM gates in that chunk are starting to wear out. You would have to use forensic means to recover this information but it still remains. The only way to guarantee that the information cannot remain on the disk is to use encryption and make sure that the unencrypted key never touches the disk.