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The irreversible global catastrophe is imperialist militaries massacring people with little risk to themselves. 
The irreversible global catastrophe is assembly line robots at the Toyota plant becoming sentient and going on a freaking epic terminator style mass shooting and enslave everyone except me 
It doesn't make financial sense to manufacturer a car or computer that lasts 70 years because of rapid technological progress. There are some 50s cars still driving around, but they're cool toys. Worse gas mileage, worse emissions, worse handling, no airbags or ABS, etc - for all the practical uses of a car, modern stuff is better. Same for computers, try browsing Hexbear on a UNIVAC.
Replacement parts are an engineering choice. Over the design life of the system, usually it's cheaper to say "swap these relays every 10 years" than to put in a huge durable relay that will probably last for 75. You'll find some elevator computers and other industrial controllers with long lifespans, but pretty much the only systems you will find no replacement parts are things like the Voyager probes.