Because they had new surveillance technology (the telephone) and they needed a plausible explanation for what the source of all their secret information was. Yo

Because they had new surveillance technology (the telephone) and they needed a plausible explanation for what the source of all their secret information was. You can turn a specially modified telephone into a listening device. All important people had phones in their offices sitting right on their desks. But obviously, to the gullible public, they were getting it directly from “the dead”.