There was a period of time before plastic was invented, during which the only cable jacket was lead.
Most "pre-war" (between WW1 and WW2) city buildings had lead/pulp house cables (risers from the basement to floors) and local cables (horizontal on a particular floor.)
Later, there was a transition to PIC in feeders, risers, and horizontal cabling.
There are still many millions of feet of lead cable still in service, in buildings, in the ground, in ducts, and in the air.
The people who knew how to trouble-shoot and repair them are all pensioned off, along with the tools and knowledge. The phone companies are relying on a business model of going out of business before they need to replace the cables. Verizon's Chairman said that a few years ago, when he announced that copper phone service was dead and his company was now focusing on cellular service.
