Why are solar DC string cables considered special cables?

Solar DC cables are exposed to outdoor conditions for many years.
They must resist UV radiation, ozone, temperature cycling, moisture, and mechanical handling during installation.
Solar cables also operate in DC systems, where arc behaviour and insulation performance are different from many AC circuits.
Ordinary flexible cords should not be used as a substitute for PV string cable unless the required DC voltage, outdoor durability, and standard compliance are fully proven.