Mainly because I know how people were during the cold war and have no doubt in my mind that the thought process was "nobody will ever access this without a reason, so let's make it super quick and easy or we might be radioactive slag before we finish typing"
One of the things they teach in cyber security is to assume that no matter how much you bang on about secure passwords the client is still going to have Password1234!. So you build around that.
Though people were a lot more blasé about security in general in the cold war. Computers were considered to be quasi magical boxes and it was sort of believed that they wouldn't act against you.