"Not sure why you think a load of extra moving parts is going to be more reliable than some solid state electronics.“Because cars can go anywhere including right outside tow truck range especially where I live. Here, being rescued can be days away. Then there's the adverse conditions, temperatures well in excess of 40° C and from my bitter experience, the electronics fail much more frequently under these harsh conditions than do the mechanics.
Then there's the issue of make-do. When one is hundreds of miles from anywhere, one can often improvise a mechanical repair whereas it's nigh on impossible to quickly sort out an electronics problem (unless it's trivial).
I recall being in a convoy of four cars in central Australia when the computer failed in the one and only Volvo in the group. What an unholy mess that was. None of us could fix it.
Note, everyone in the convoy was skilled in electronics (we were all radio amateurs on a field trip) and almost everyone had a full-time professional job in electronics. We even had lots of electronics test equipment as well as various electronic components with us
- semiconductors, resistors, capacitors etc., as they were to service our HF transceivers when they failed.
That's just one instance albeit one of the worst cases.
My car chucked a universal joint on the same trip and although very inconvenient, we fixed it on the spot. Similar repairs were made on the spot when my petrol pump was ripped clean off the bottom of my car by huge ruts in the road.
From what you've said, I'd guess you live in a temperate climate in the suburbs of a city and only a few kilometers from a service garage.
The fact is, electronics and harsh environmental conditions (high thermal cycling) are not good bedfellows. Moreover, most electronics faults are thermally related (caused by thermal stress). I know firsthand as I ran the electronics department of a large corporation for years, before that I worked in the prototyping (design) department of a large US corporation designing professional electronic (not domestic stuff).
First rule of design: 'keep it simple stupid'.
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Edit: "1970s, the typical car reached its end of life around 100,000 miles (160,000 km)."
Uh? When I was younger all I could afford were cars with over 150k on the clock - and that's miles not kms - and I usually drove them to about 300k. The usual reason for getting rid of them was was rust - not because of mechanical problems. Sure, there were 'junk' cars around but you'd have to be mad to buy one.
One final point, around the time the Volvo broke down I was averaging 44,000 miles per year (~70,000 km/yr).