You are lucky, or bought the right brand of drives at the right time.
I had five new Seagate 7200.11s which had an easy life but not make it past 22 to 25k hours before they started failing en masse (and thats not even counting their firmware bug that got me). ZFS RAIDZ1 (RAID5) pool, which survived a second drive starting to fail while rebuilding from the first failure. It was that event that made me love ZFS forever.
Contrast to my WD Reds which are 52k+ hours without errors or issues (no failures in a set of 8). And some HGST refurb drives that are at 70k+ hours (some failures in a batch of 14, but they were refurb with wiped SMART data so the failures werent unexpected).