If you look at wars during the Antiquity, barbarians would rush to combat in disorder. They would challenge each other to kill the most enemies to keep themselves motivated. And they were utterly decimated by the roman legion. Hierarchy replaces morale with discipline: centralised armies can push soldiers way beyond the point where they would give up and flee if they could. Therefore, trust is less an issue in centralised armies: each soldier can be assured that their neighbour will not leave their side at the worst moment. This in turn boosts the soldier’s morale. Unorganised armies would rush to combat, but also break and flee easily, which made it easy for fast troops like cavalry to chase and slaughter them.
Also, strategy: sometimes, troops must be sacrificed to make a higher gain. Who would volunteer to be sacrificed?