Paintwork can, in some cases, become oxidized. Making it turn matte and slightly fade color. If untreated, it can eventually cause the lacquer and/or paintwork to completely fail. It is most common on red cars, but it can happen with every color.
Not all coatings have enough effect on the oxidized look of UV-damaged plastic. Most dressing restore the look better, but don’t offer the protection of a coating. Combining these 2 seems illogical and difficult, but it isn’t.