A 486 system was built before the capacitor plague. Quality electrolytics may not last forever, but can last a long time. Also, built before RoHS and the reduced longevity of poorly formulated or poorly applied lead-free solders that were common for many years.

Processors had less protections, and thermal monitoring was at its infancy because almost all the 486s wouldn't use enough power to cook themselves to death, even with passive heatsinks.

I don't know about memory sticks and hard drives from that period. It's quite possible they've replaced the hard drive with compact flash or something too, which should be pretty reliable given they apparently only make a floppy disk's worth of data every day.