Turn of the nineteenth century machinery (of any sort: woodworking, metal milling, ect) and up to the 1940s were designed and built to last forever. Everything was properly forged, hardenned and machined, or if castings were used, were of very heavy and careful nature. Aside from the CNC function that are available now on new machines everything else mechanical is inferior to the past and design to be cheap to build. Lots of sheet metal stampings, drawings and resistence weldings. Longevity is no longer part of the equation.
The plain honest truth and wonderfully explained to boot! You have to wonder if the same principle had been put to work in the space probes whether there would have been any accidents.