Although your vehicle’s manufacturer – General Motors, in the United States – agrees with you that brake fluid never needs to be replaced (partly because it contains certain additives), the situation in South Africa is somewhat different: over here, the company certainly recommends the periodic flushing of old fluid for safety reasons.
Their official response: “Vehicles produced by GM South Africa are all pre-filled with DOT-4 brake fluid. Since brake fluid is hygroscopic (that is, it absorbs or attracts moisture from the air), and since the presence of elevated levels of moisture reduces its boiling point, GMSA recommends its replacement every 24 months.” But there’s a second issue. The brakebleeder bolts in the callipers or wheel cylinders will eventually freeze in their threads if they are never loosened. If it ever becomes necessary to bleed the system, they can be difficult to remove.