Front Seat Belt Anchorage problems of the 1998 Dodge Ram 3500

The seat belts will not extend. The dealer advised that the little pin is broken and will not let the belts extend. Why would this pin become defective? why would both seat belts have the same problem at the same time? the passanger side is rarely used. This problem was noticed when the vehicle was new but I thought it was the temp. In the truck which was rather high. The dealer advised the costs to replace the seat belts would be over $600. 00. These should not go bad and become unusable. Dt.