RODC exclusion – Why?

Why do cargo underwriters include ROD or RODC exclusion in the policies? Rust, Oxidation, Discoloration & Corrosion are perceived as gradually developing flaws which cannot be co-related to a single event during transit. Even without this specific exclusion, they would still fall under General exclusions under the ICC clauses.

Some exclude RODC absolutely, which is understandable. Whatever causes the RODC, the loss will not be paid. Unreasonable to the insured. If a steel coil falls into a river during transit and is fished out after a couple of days but gets rusted. No claim under an absolute exclusion. Some underwriters recognise this and word the exclusion to say ‘ unless caused by ICC-B perils.’. An improvement but still does not reflect the intent which is to exclude RODC arising out of natural atmospheric conditions. What if there is a leakage in the ballast/ water tank on the vessels leading to steel cargo getting wet and rusted? No claim, because ICC-B peril has not operated. Better option would be to exclude RODC unless caused by accidental, external means. Fair to both parties. Question still arises if prolonged exposure to rainwater causes rusting, will it be covered. My thought is No, as rainwater may be external but not accidental.