I'm afraid we might just have to agree to disagree on some of this.
Certainly you're right that modern cars are more reliable, and the better built-in diagnostics are a part of that. But the flip side is that you used to be able to buy a repair manual for any major model of car and take care of it yourself, and if you did then many popular models could last almost forever. Today it's barely possible to change a light bulb or diagnose the cause of a simple warning light in many new models without going to see your dealer, a term for the official representatives of the car manufacturers with other connotations that also seem all too appropriate these days.
As for the modern electronics you speak of, I fear you're suffering from much the same perception bias you think I have. A lot of devices made the best part of a decade ago were pretty reliable, but standards have dropped sharply even as recently as the past 5 years. My previous washing machine also lasted about a decade with a couple of minor repairs along the way. Talking to a surprisingly honest salesman when buying the new one, he said only certain prestige brands would expect that sort of longevity today, and with most of the mid-range models you'd be doing well if it was still economic to maintain them beyond 5 years. I never had a PC fail on me before being retired after many years of use until about 2010. I haven't had a single PC, at home or work, of any spec, last beyond about 3-4 years without at least one serious hardware failure since then. My previous DVD player lasted many years. My current Blu-Ray player, a relatively expensive model at purchase, is already starting to fail after maybe three years. Printers. Phones and tablets. TVs. PVRs. Headphones. Networking gear. Almost no technology is built to last these days, except perhaps for some of the high-end prestige brands, and many of the electronic devices in my home and office come with some element of built-in obsolescence that is entirely artificial, often due to legal controls on replacement parts and interoperability, or to dependencies on software or online services that aren't supported for very long.
I'm certainly not saying that everything we made yesterday was better made in every way than what we produce today, but junk that fails after what used to be considered a very short lifetime, often for entirely deliberate and artificial reasons, and with limited or no prospect of servicing or repair to restore it to use, is mostly a very modern and very unwelcome trend.