The article said that the failed hard drives were completely dead, despite them having been used very rarely and being stored in archival conditions. To me, that implies that the drives failed not due to the degradation of the magnetic fields on the disks, but rather due to manufacturing quality defects, because it sounds like the spin motors simply refused to work. That can happen, for example, if the seal on the lubricants in the motor were faulty, allowing the lubricants to dry out. Another possible cause is if subpar components were used in the control circuit board, allowing them to abnormally degrade over time and cause the board to completely fail to work, preventing the spin motor from running..
If the spin motors had worked, the hard drives would not have been completely dead, but rather would have still spun and allowed at least some of the data to be read, if not all. I read some technical papers a while back that stated that the magnetic disks in the hard drives should be able to retain data for well over 10 years due to how the data are magnetically recorded. To give you an idea, it requires a very strong industrial magnet held up against the hard drive to damage the data. Your run-of-the-mill toy or refrigerator magnets are not strong enough to cause any damage to the data stored on the disks. Still, since there is no way to predict how reliable the mechanical and electrical parts of the hard drives are, you should take additional actions, such as storing the important files in multiple drives made by different manufacturers, to reduce the risk of losing data due to a failure of any one hard drive.
It also helps to store the files only in the hard drives that have had good reliability track records. Google, for example, has released data on which hard drive manufacturers produce the most reliable drives, based on the the failure rates of the drives it uses in its data centers around the world.
Personally, I have hard drives from well over 20 years ago that are still running like champs. But I also backed up the files that are on those drives that I want to keep, since I have no way of knowing when those drives will start showing signs of degradation.