Why did Wellington criticize his troops after the Battle of Vitoria?

Following the Battle of Vitoria on June 21, 1813, Arthur Wellesley, 1st Duke of Wellington, criticized his troops because they became distracted by the vast amount of French baggage and spoils captured during the rout.1

Instead of pursuing the retreating French forces into the Pyrenees, the soldiers prioritized looting the "glittering prize" of the enemy's abandoned supplies, which allowed the French to escape. Frustrated by this lack of discipline and the missed opportunity to decisively finish the engagement, Wellington famously denounced his drunken troops as "the scum of the earth".1