And they are old, because of many certification requirements set partially by the industry, and a few odd governments.
In reality, most of them are both less reliable, and harder to work with in comparison to open market parts.
The only two things I seen chips with micron scale nodes used in my life were: air conditioner boards, and car parts.
I mean, worst case, when you let go of the starter motor, it creates a huge back EMF. Imagine your chip finding its +5 input suddenly 12 volts below ground for a significant fraction of a second. (Now, it shouldn't be that bad any more. That was back in the bad old days, when chips were just starting to be added to cars. Shielding should be a mostly-solved problem these days. But is it solved well enough for your 7 nm chip, or just well enough for the micron-scale chips? It's something you have to really carefully look at before you move to smaller processes.)
For as long as you talk about digital side, you can. Your smartphone is a way more noisy electrical environment than your car.
Cellphones are are certainly tricky, but in a different way than cars. In my experience with EMF measurement and EMI compliance at Underwriters Labs, cars are uniquely challenging due to the relatively strong EMF generation from the huge number of motors, solenoids, coils other magnetic bits banging around and interacting with each other in hard-to-predict ways.
A smart phone is not a "way more noisy" environment than a car. It has different issues, and frankly a far more constrained and predictable environment. A load dump event in a car can take the 12V supply over 100V. I have never heard of that in cell phone. Long wiring harnesses are a nightmare and require careful design. It is hard to compare a cell phone and car without a clear definition of "noisy", but as someone who has designed systems similar to both, I think the car is a harder set of problems. Just not as constrained noise sources or components.
When a failure can kill someone, you have to take it much more seriously than when a failure slightly inconveniences a user while they restart the app.
Cars still use micron level chips because:
- They still do the job.
- They have enough volume to keep those fabs open.
- Since they end up becoming the only buyer (monopsony), they get cheap rates.
So they pretty much run those fabs to the ground.