People who let rare cars rot.

It depends where you live as to how fast and how a car will deteriorate...

I am in a prairie desert, my scrap has less rust than most of the cars in the rust belt, but on the flip side I get sun baked crumbly rubber and plastic pieces.

That said, I am not going to worry about a car with zero rust being outside here. The interior and seals were trash before I bought the car and the metal isn't going anywhere.

Around here you leave the trunk lids open so the air can dry them out after it rains, twice a year.

In the rust belt it will be a far more urgent matter, by having a car outside next to a barn