Even in my own case, the closest I ever came to gaining such knowledge in my formative years was in a high school psychology course where I learned about paranoid schizophrenics and manic-depressives, but not much about normal people. Without any formal training to fall back on, we learn to manage by following the model set by our previous managers. Most of us were likely mentored by managers who grew up with a cop mentality. That's what they taught us because that was all they knew. This model of supervision is a lot closer to law enforcement than it is to enlightened leadership.
Cops go out looking for problems to solve.
Cops see most people as crooks who will rob them blind if they don't watch them every minute. Cops believe that they can push employees to perform and that they can motivate with fear. Following the cop model, many people try to force their staff to perform and expect this approach to work. I don't know if the cop model ever really worked although I will grant you that there was a time when we could more easily get away with it. In fact, being a cop is seldom effective in the long run because it is an external and not an internal force and does not properly address the human factor.