The phrase is rooted in a very old memeplex, the part where religious morality and sociopathy overlap. Most ideas revolving around the concept of "putting the fear of God into someone" aren't actually for regular people with empathy. They're for sociopaths. It seems that sociopaths used to be seen as just completely normal people, undifferentiable from everyone else—and much of "morality" is actually an attempt to create extrinsic incentive systems to replace the thing that sociopaths lack, so they can seemingly function normally.

That's all to say, by analogy: locks are to keep honest-acting sociopathic opportunists honest-acting.