You would think that but at least with the 8tb version they are often standard red drives that look the exact same as any other. It could be just that since they are their own drives, they can afford to price the hard drives much closer to their manufacturing costs.

I think it's standard price discrimination— internal drives are often bought alongside other expensive equipment as part of a "build" so that purchaser is a lot less price sensitive overall than someone who walks into Best Buy looking for a USB3 drive to use with Time Machine.

Or the drives could be refurbished, returned or otherwise unable to be sold as new. Based on the pricing, that always seemed like the most likely explanation.

The cost cutting comes from the warranty. You would have to send back the whole disk with the case as opposed to just RMA a disk.

Worth checking the model before doing so - I've had at least one drive where the USB connection was built into the drive itself (i.e. no SATA connection). I think it was a 2.5" drive, but I'd presume it's at least possible with a 3.5" drive.