Did you happen to look at the date code for these HDs?
I am still trying to verify what subset of external HDs don't have the USB bridge.
All drives were manufactured 11 SEP 2016. So fairly recent.
Why are external drives so much cheaper? They have more parts therefore they cost more to make. Is it simple supply versus demand to cause the external drives to be cheaper than internal ones?
No bloody clue. The thing about the ones I shucked, they weren't just a couple bucks cheaper and I was being a miser about it... but the 8TB drives I ordered were anywhere from about $70 to over $150 cheaper.
The drives I got were HGSTs whitelabeled to be WDs. 7200rpm and TLER can be modified, too. Granted, there's a little gambling involved. You might get HGSTs, you might get WD Reds or Blacks, depending on the batch. But most people report HGSTs. Either way, still cheaper than getting any of the other three.
WD My Book 8TB: $229
WD Red 5400 Rpm 8TB: $327
HGST Deskstar NAS 8TB: $329
WD Red Pro 7200 RPM 8TB: $447
HGST Ultrastar He8 7200RPM 8TB: $526
Huge difference in pricing there for what you get in the My Books and shuck. Same body, same label, same specs as the Ultrastar.