Yeah pretty common thing across all industries. I would expect things like maybe the vibration is slightly out of normal spec, or an abnormal amount of bad sectors on a fresh unit.
But I don't understand how them maybe not being top quality would make part of the SCSI protocol disappear in the firmware. That indicates that these drives had a different firmware developed for them with missing features which makes no sense.
What you are missing is that WD Passports are 2.5 inch drives that are USB-only. The drive controller speaks USB directly, as opposed to SATA chained to a translator chip on a separate board.
They implement certain parts not pass through and do indeed have separate USB firmware.
But I don't understand how them maybe not being top quality would make part of the SCSI protocol disappear in the firmware. That indicates that these drives had a different firmware developed for them with missing features which makes no sense.