SSDs are just limited write cycles whereas HDDs literally spin themselves to death. In a simple consumer NAS usage, like if this was just photo backup, that basically means SSDs will last forever. Meanwhile those HDDs start hitting borrowed time at 5-8 years, regardless of write cycles.
I have had two Sandisk 2.5 inch SSDS just suddenly fail. No warning that I could discern, and no way to recover afterwards. Both were while running Debian variants as a / partition, luckily I keep /home on a separate partition.
Any idea what that failure mode could have been? It worries me tremendously to keep data on an SSD now.