First, the partition boundaries and data are represented by magnetic patterns, which will decay with time. How much time I don't know and I suspect nobody truly knows because actual time is needed to develop useful data. Simulations are no substitute for actual time measurements. I have used floppy disks that are more than a decade old that according to many people should no longer be functioning.
Second, electrolytic capacitors are subject to deterioration. Long periods of non-usage allows the electrolyte to dry/evaporate. Continual electrical usage maintains the insulating layer and "reforms" the capacitor. Reforming sometimes is possible but for most people impractical. Periodic usage therefore is good prevention.
Third, as mentioned, there are the bearings. Although hermetically sealed, I suspect that with significant periods of non-usage the lubricant tends to harden. Most modern drives now use fluid dynamic bearings, however, so this concern might not apply to such drives.
An annual maintenance chore of powering up these devices is a safe precaution. I do this annually with some of my old electronic equipment sitting on the shelf. Unfortunately, I had strayed from my old photography hobby for several years. Last year when I tried my Speedlite 177A flash unit, the device refused to fire. Sat too long in the camera bag in the closet. I don't know the exact failure, but I am willing to bet a beer the electrolytic capacitor is dead.
With that said, I have been using hard drives for backups for years. I gave up on cumbersome tape drives, CDs, and DVDs long ago. I use a drive bay. Backups are a manual operation, but full automation never was a high priority for me.
However, for your purposes --- storing music albums, I think DVDs would work just fine and as mentioned, much less expensive. If deterioration is a concern, then every two years recopy and test the DVDs.
This kind of talk is FUD intended encourage people to buy more hard drives.They even told them that a disk has only a couple of months of life if they are stored offline and never powered up.
I have old hard drives that still fire up just fine and they sit on the shelf for long periods. My oldest drive is a 512 MB Conner from 1991. Still works and I fire up the drive only once or twice a year.