Brake fluid is hygroscopic... it will absorb moisture over time. This is why it needs changing every 24 months regardless of how much the car is used. Without properly functioning brakes, you are not only a danger to yourself, but other innocent people on the roads.
I never reach the KM limit for my services, so I get them done every 12 months, which should really be the minimum to ensure that the car is in optimum condition and will live for longer.