When I went to college in the late 80s my ssn was automatically used as my student id. When I got my first bank account in 1990, they used my ssn as the account number.
Ah it was a different time. Societal trust was greater. Without global internetification, the only people who could ever have any opportunity to exploit this information were your fellow campus denizens (students, professors, etc).
Without global internetification, there was not as much an average person could really do or would know to do with an SSN alone to exploit it.
This story is a good parable for so much of what has changed in the world the last couple decades -- we had a world built for less globalization, then we globalized, and we've been gradually adapting to / dealing with the unintended consequences since then.
A real life door can only be picked by your neighbors or anyone else nearby -- attack surface is limited by the nature of physical distance.
A virtual door can be picked at by 7 billion people.
Go Jackets.