"A crusade army was, in effect, a loosely organized mob of soldiers, clergy, servants, and followers heading in roughly the same direction for roughly the same purposes. Once launched, it could be controlled no more than the wind or the sea."
The petty lords...and knights were independent and their allegiances constantly shifted as circumstances changed and the ability of princes to reward them and their little entourages came and went. [Jonathan Riley-Smith, The Crusades: A History (New York: Bloomsbury, 2014) 62-63.
During the First Crusade there were four different attempts to designate a commander-in-chief, and had the Byzantine Emperor agreed to lead the campaign he would undoubtedly have assumed this function without dissent -- but he didn't. None of the western leaders, however, was strong enough to either intimidate or inspire the other princes to subordinate themselves to him.
The Second Crusade notoriously nearly fell apart because King Louis could not agree with the Prince of Antioch on a goal. The Third Crusade was weakened by the bickering between Philip of France and England of Richard, and later by the French refusal to follow Richard. The Fourth Crusade was characterized by assemblies at every stage along the way at which everyone discussed what to do next. With each decision that took the crusaders closer to the sack of Constantinople, more crusaders refused to follow the leadership and struck off on their own. The Fifth Crusade was riven by rivalries and bitter fights over strategy and spoils between the pope's representative, the Holy Roman Emperor's deputy and the King of Jerusalem. The Sixth Crusade saw the absurd situation of an excommunicated Emperor unable to command the forces of the military orders and alienating the local barons into revolt.