Here is someone that had significant corruption until they stopped: https://www.xda-developers.com/why-not-to-spin-down-nas-hard...

There are many similar articles.

I wonder if they were just hit with the bathtub curve?

Or perhaps the fact that my IronWolf drives are 5400rpm rather than 7200rpm means they're still going strong after 4 years with no issues spinning down after 20 minutes.

Or maybe I'm just insanely lucky? Before I moved to my desktop machine being 100% SSD I used hard drives for close to 30 years and never had a drive go bad. I did tend to use drives for a max of 3-5 years though before upgrading for more space.

I wonder if it has to do with the type of HDD. The red NAS drives may not like to be spun down as much. I spin down my drives and have not had a problem except for one drive, after 10 years continuous running, but I use consumer desktop drives which probably expect to be cycled a lot more than a NAS.