It's just game theory in action.

People with morals, principles, integrity, honor and/or empathy will exercise self-restraint - there are choices they will not make and courses of action they will not follow.

Those without those qualities will not be so constrained. They can and will do absolutely whatever it takes to gain whatever they might want.

So all other things being more or less equal, psychopaths actually have a competitive advantage in systems of institutionalized, hierarchical authority - governments, corporations, police departments, armed forces and so on. For all intents and purposes, those institutions reward and thus select for psychopathy.

It's sort of akin to the way that cancer spreads through an individual by outcompeting, dominating, displacing and destroying healthy cells.

And it's just as ultimately fatal, and for essentially the same reasons.