My theory for that is different construction materials: cars built in the 1970s and 1980s become rust-buckets quite easily - but cars built after the mid-1990s

My theory for that is different construction materials: cars built in the 1970s and 1980s become rust-buckets quite easily - but cars built after the mid-1990s use considerably better bodywork materials that don't need specialist care to maintain, especially a lot more plastic. I drive a 2013 Ford Focus and the entire front assembly is plastic - no way that's going to rust or corrode. I'm almost looking forward to selling it for a good price after the warranty expires.