My guess is it was poor conditions or materials during the manufacturing process. Clearly a significant number of components were made that have failed but not until after the system was off the market for some time. But to us and by comparing with other systems it's still premature failure of components. Who knows what sorts of problems they may have had when making the chips. About the rubber belt, I would think that semi frequent use might keep it from getting hardened and brittle as fast. But in theory you should be able to replace these belts. People replace belts on Famicom Disk System drives so why not the Panasonic Q.
I don't really think it matters since the band being stretched is a constant force. the only drives ive had develop this problem are the ones i've used the most. As a matter of fact vacuum cleaners use similar mechanism with a belt, and how much I run the vacuum cleaner is pretty consistent with how often I have to replace the belt.
I have also read somewhere that is better to use HDD's regulary, because if you leave them unused for a while (I mean months and years), the head can somehow damage the magnetic discs. It is especially true with older PC's and consoles like the OG Xbox. Don't know how true this is, as I never had a Hard Drive fail, even very old PC's that have been left for years still work. Any thoughts about this?
I have a strange problem with my one SNES where I believe something was corrupted. For Link to the Past the beginning Tri-Force logo shows up incorrectly and on Home Alone 2: Lost in New York the backgrounds don't scroll correctly.
May be just a coincidence, but I put one of my laptop HDDs into a new enclosure before I was enlisted into the army here in 2013. In 2015, I went back to study... and found the HDD dead (unable to spin up).
SNES consoles are known to experience chip failures that lead to all sorts of problems. Games may still run but have a range of glitches. In my childhood SNES one of the two PPU chips experienced a failure related to sprites. It results in vertical lines in sprite cells. There is no way to fix it other than replacing the PPU chip with one from another console. Besides PPU chips failing the custom CPU chips are known to have failures. I'm not sure but consoles manufactured later and perhaps the so called OneChip consoles may have a better reputation for reliability than older ones. My console that failed was an older model.
My recommendation is not leaving AA batteries inside controlers. They tend to leak and can destroy the insides. Happened with my Wii Remotes several times.