"Everything from the design process to the assembly and repair is completely different today than it was 50 years ago."1. Yes, and that needs to change—and very soon at that. A short while ago I counted over one hundred x86 motherboards that were current and readily available from just one single manufacturer. I spent many hours trying to differentiate the minor—almost insignificant—differences between many of these boards (in fact, most of the differences were essentially trivial).
This nonsense is a deliberate marketing ploy and there ought to be definite penalties against it. It wastes considerable time and human effort that ought to put to better endeavors; confuses buyers as well as those who have to get the equipment working (let alone repair it); and it also screws up the development of software drivers—as no one is ever quite sure what all those minor changes are all about—and manufacturers haven't the time, wit or inclination to resolve such matters let alone spending time on providing upgrades for a PWA/board that has such a fleeting lifespan. No wonder the world is awash in e-junk! [That's just the beginning of that narrative but I'll spare you the rest.]
2. Then there are the thousands upon thousands of bugs that slip through software development and that are never fixed due mainly to the fact that the compilation process obfuscates them all and that there is no law or obligation to compel the developer to provide the source code that would reveal the underlying spaghetti code (this is the modern equivalent of a doctor burying his mistakes). ...Now, how many hundreds of examples would you like me to cite?
3. "At the same time, consumers stopped caring about repairs." That's true but fortunately they've now changed their minds—mostly because disingenuous manufactures have made either substandard equipment or equipment that has been deliberately designed to conform to the manufacturer's planned obsolescence strategy (I suggest you read my comments of several days ago on the Phoebus Light Bulb Cartel (BTW, it's still effectively alive and well)).
The sooner goods that cannot be easily repaired—or that are found to be deliberately designed to aid a manufacturer's planned obsolescence strategy—are taxed the sooner they'd fall into line. The classic example of this caper is the notorious—diabolical—example of smartphone batteries that are deliberately designed not to be changed. No wonder the Right to Repair movement has gathered apace and that new laws to regulate such wayward behaviour are now pending. Smartphone design would change overnight if every smartphone whose battery was not removable was levied with a hefty e-waste disposal tax! The same goes for smartphones whose manufactures deliberately disable the FM radio circuitry (a tax or levy on this can easily be justified from an emergency stance: if cell towers go down in floods, bushfires, earthquakes etc. and the FM radio works then phones would have at least some basic connection to the outside world). Right, that one's a no-brainer that everyone ought to understand!
4. With respect to your comment about JIT, it was alive and well when I was working in a manufacturing plant in Japan around the time that I was referring to.
Incidentally, I have worked in manufacturing and specifically in an electronics prototyping laboratory where much of my time was involved in liaising with production. I know the arguments you are putting very well, and whilst there is validity to some of them, many are just opportunistic and have been done more to benefit a manufacturer's coffers than to benefit users/consumers.
Thank goodness that's about to change.