Why do optical cables need coils?

Optical cables are not like cables, which are made of metal and can be joined together by a metal core or by welding and crimping. The core of the optical fiber is made of glass. The glass needs to be extended even if it is shorter, it also needs to be fused, and the welding work is much more complex than the connection of the cable, and it needs professional equipment to complete. Cable has so many plates, fused cable cable, buried silicon core tube bending, and the rules of the industry are in accordance with the length of the cable settlement costs and other factors, cable construction personnel, often left hundreds of meters in the joint box next to the plate, I have found plate left more than 500 meters of the joint box. With so many reservations, it is impossible to find the attenuation location with OTDR alone.