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.
This! Got a used AMD-K5 PR133 in a big-tower a long time ago, integrated it into my home lab, and used it to experiment.
About 1 one year later it underwent my cleaning routine, vacuuming dust out, cleaning the fans, etc. I took the cpu-cooler off to check for bad thermal grease and discovered it had none at all! No pad either, someone just clipped that thing on, and instead of direct contact it had a small airgap which you could look through from the sides.
Unbelievable.
When I got it, it must have been in use for years already!
Um.... All electrolytics eventually go bad as the electrolyte solution dries out eventually. Re-capping retro computers and radio gear from the 70s through the 90s is very much a thing.
That being said, electrolytics were somewhat less common than they are now. But the Capacitor Plague is not the only reason electronics are recapped, especially older/vintage/retro electronics.
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.