general problems of the 1999 Chevrolet Silverado

Parking will not "hold"when applied. I live in the "flat land"of georgia so I never use this brake,park gear is sufficient. I took truck to dealer and had rear wheeles "pulled"and inspected. . The parking brake shoes were completly wore out. As I don't use these brakes,no one could explain how this could happen. . And as truck is out of warrenty it would 250. 00 to replace shoes. Iam curious and as well apprehensive to replace or repair some thing that I don't know how or when it "wore out"when it's not used!!!.