Yes. Originally ARPAnet (Advanced Research Projects Agency) was conceived as a network between large universities, the government, the military and government contractors. Basically a bunch of friends and aquaintences. Security really wasn't a consideration until after ARPAnet was opened to the public.
That's because these message clients do not use end-to-end encryption.
End-to-end encryption is nothing more than a security feature used by application administrators. With this feature the system aims to encrypt (encrypt the message to make it unreadable when stored) at the two "ends" (people who are talking) of the message.
