For the same reason that everyone used the Knights Templar or Venetian bankers to pass messages and money.
EDIT: And you’re talking only 100 years ago. We had radios, telegraphs and telephones 100 years ago. It was reasonably common knowledge that it was possible to listen in on those even if you weren’t the intended recipient. Heck, part of the plot of The Count of Monte Cristo (1846) involves hacking a telegraph system with a MIM attack to manipulate international financial markets.
For the same reason that everyone used the Knights Templar or Venetian bankers to pass messages and money.
EDIT: And you’re talking only 100 years ago. We had radios, telegraphs and telephones 100 years ago. It was reasonably common knowledge that it was possible to listen in on those even if you weren’t the intended recipient. Heck, part of the plot of The Count of Monte Cristo (1846) involves hacking a telegraph system with a MIM attack to manipulate international financial markets.