For example right now in Germany I can get a WD 8TB USB 3.0 drive for 135€ but the cheapest internal 8TB drive costs 169€.
Any idea why? It's puzzling.
https://www.instructables.com/id/How-to-Fix-the-33V-Pin-Issu...
In large ZFS arrays, many people are using them with great success, at no greater or lesser annual failure rate than the expensive enterprise hard drives.
I've read these reports as well, but I can say that it's not my experience (we've gone through a few rounds of shucking at the Internet Archive, for economy and in one case necessity after the 2011 Thailand floods pinched the supply chain). Our raw failure rates on shucked drives are significantly higher, and the drives themselves are typically non-performant for high-throughput workloads (often being SMR disks/etc, though hopefully the move away from drive-managed SMR will finally kill that product category off).
Shingled magnetic recording (SMR) is a magnetic storage data recording technology used in hard disk drives (HDDs) to increase storage density and overall per-drive storage capacity ... The overlapping-tracks architecture may slow down the writing process since writing to one track overwrites adjacent tracks, and requires them to be rewritten as well.
Of course, that wouldn't explain the difference between a WD external drive and that same drive as an internal drive - assuming that WD actually manufactures both (and doesn't just license the name provided the 3rd party uses their drives)...