12 years average means there're plenty of 20 year old cars. And many old cars stay on the road, just exported to poorer countries.

No they don't. They spend very little time on the road, most of the time stationary. Obligatory link to Donald Shoup and the "High Price of Free Parking". https://en.wikipedia.org/wiki/The_High_Cost_of_Free_Parking

My cars are all older than that and they are still pretty awesome.

Subaru and a Highlander. Not particularly valuable but they get the job done for my family and I for A-to-B.

Outside of Silicon Valley, I see a lot of old cars on the road.

The above poster used a referenced published average and you responded with your 2 hyperlocal anecdotes.

Averages are averages, medians are medians, and anecdotes are not data.

Sure, lots of people just want a newer car and can't or don't care to reuse or recycle.

If someone is disposing of a perfectly good used car to buy a new car, then someone else is going to buy their used car. And if they sell their old car and it's still decent, someone will buy that too. On down the line until you get to a car that isn't worth owning. And then that car is largely recycled, which is a better use for it than staying on the street polluting. No one is throwing out working electric cars, or gas cars that get good mileage and are in good operating condition.