You are right if the annual mileage is high, otherwise rust on the body is most likely reason to end the life of a car.

 

Pretty much all the cars I have ever owned were scrapped because of rust. My Camry was 34 years old when I scrapped it. Near the end I was jacking up a corner of the car to change a tire and the jack just went right through the metal. That was at a jacking point too. Still kept it for a little while longer until an electronic ignition module went. Replacement was available on the aftermarket but it was time to let go. Bought the Fit a short while later.

I used to believe that manufacturers had to make replacement parts available for 10 years but that's not true. They're really only required to have parts available to cover the warranty period of the car. That's typically 5 years at the most.