I don’t agree with the idea that cars have to be aluminum or carbon fiber or fiberglass to be rust free.
All cars can be corrosion resistant to the degree that they will last as long as you want with the right maintenance.
In addition, I feel that Stainless steel, with a minimum of 10.5 or 11% chromium is also very corrosion resistant, may cost too much for car bodies, but adding lesser levels of chromium in varying levels to different parts as required can very cheaply add to a car’s longevity. Aluminum and fiberglass present problems of their own so that steel has remained the material of choice. Rust is a car manufacturer’s friend, and much research has gone into, not preventing rust, but controlling it at an acceptable level for the consumer and the turnover routine requirement for car maker profitability.
Besides, I would argue, rusting of non structural components does enough in the appearance of car ownership to insure safer cars are rotated into service. All are bean counter decisions and not your or mine. Just make a concerted effort to maintain a car body with the same eagerness we give to the “way too often discussed” oil change interval, and your car will outlast your desire to keep it. Make it worth much more at trade in time too.