Ice tends to stick to a lot of things as it freezes, including many of the waxes used in car polishes and paint. But if it sticks to the polish, then the outer layer of the wax peels off easily, so the ice comes off together with a fraction of the wax. If there is no sacrificial material on the paint because dirt, grit and the like have disrupted the protective wax layer, then the ice sticks to the paint itself, and is harder to remove.

Go well,

Jon