Earlier quoted context omitted.
You are correct in that hard drives are still an order of magnitude cheaper per unit of storage than solid state drives. Then again, tape drives are still an order of magnitude cheaper per unit storage than hard drives. When was the last time you saw a tape drive?
Where do you think Amazon Glacier data are stored? There's no point storing that on a high-IOPS, always-on medium, like an SSD or even HDD . Tapes are big, and still make complete sense for backup purposes, especially if you want to maintain latest 10-15 backup copies to choose from.
https://storagemojo.com/2014/04/25/amazons-glacier-secret-bd...