One we started using connected machines for much and people with flexible though morals noticed that there was trust in the system(s) ripe for exploitation for fun or profit or both.
I remember SMTP hosts being open by default because it wasn't a problem, that very quickly changed once spam was noted as potentially profitable.
There were accounts all over from quite early on, in academic environments before businesses took much of an interest, if only to protect user A from user B's cockups ("rm -rf /home /me/tmp") though to some extent also because compute time was sometimes a billable item, just not on single user designed OSs¹.
[1] Windows, for example, pre NT & 95 (any multi-user features you might have perceived in WfW 3.x were bolted on haphazardly and quite broken WRT actual security)
Accounts thereafter, ruined everything.