Because the internet used to be unimaginably small. It really was just a couple of researchers talking to each other. They weren't co-located (the entire point

Because the internet used to be unimaginably small. It really was just a couple of researchers talking to each other. They weren't co-located (the entire point of internetworking) so they had to mail stuff to each other, but it was more like when you send a copy of a document to your co-worker down the hall. "Hey, Jane, watcha think about this?" The first telnet (predecessor to SSH) RFC was 9 pages, including an example of the connection handshake.