#feariscontrol
#feariscompliance

It's simple to me.

If you are scared it is very difficult to think critically.

Another angle on that is the lizard brain is known to not be good with judgement and nuance.  It is good at getting you to move "now" to save your life.

Given these two notions it is clear to me how keeping people scare makes them:

1. not think clearly (easier to manipulate)
2. easier to motivate and control by appealing to the lizard brain