The Red series was originally marketed and positioned specifically for Home/SMB NAS use. I have 4 of these (the old versions from before the SMR switch) running in my Synology NAS for years, and a 5th lying spare in its original sealed packaging just in case.

When WD stealthily swapped to using device managed SMR technology in the series, they hoped that typical users wouldn't notice the change in behavior of the drives, as they assumed a small NAS would have enough downtime for the drive to manage the data being behind the scenes rearranged towards the slow shingled sections.

This assumption is not always true, but specifically it doesn't hold at all when an array has to be rebuild e.g. because of a drive failure in a raid array, as that requires writing data continuously and for a long time.

WD was caught not just using a technology that made their drives unsuited for the advertised purpose, but initially even denying that they had done so.