There's a lot of "never let your drive spin down! They need to be running 24/7 or they'll die in no time at all!" voices in the various homelab communities sadly.
Even the lower tier IronWolf drives from Seagate specify 600k load/unload cycles (not spin down, granted, but gives an idea of the longevity).
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.
Even the lower tier IronWolf drives from Seagate specify 600k load/unload cycles (not spin down, granted, but gives an idea of the longevity).