Whenever I wonder this, I always think back to wargames’ example of phone phreaking. The answer seems obvious: early hardware/software was insanely easy to exploit because hardware/software security was not a thing. It was trivial to use features in a malicious way. We’re currently in an arms race because eventually society decided it wanted computer security.

That’s not to say systems were all insecure in the past. You just didn’t trust computers to be secure.