Why was Louis the Pious destined to have troubles his father hadn't?

Louis the Pious was the only son of Charlemagne and Hildegard who survived to adulthood, so he was naturally made sole ruler of the Franks upon his father's death. Louis, however, had three adult sons between whom he sought to evenly divide his empire. As sibling rivalry and extreme power might be expected to mix, the empire devolved into no less than three separate civil wars between the sons.
It could also be noted that the two rulers had vastly different ethics and ruling styles, which may have influenced their heirs. Before his other sons' deaths, Charlemagne maintained a confederacy of sub-empires that were to be each directly ruled by a different son. The sons were also sent on trans-regional military quests to encourage a sense of unity between the sub-empires. As luck would have it, though, Louis became sole ruler and then acted in the exact opposite manner from his father. He immediately silenced and disenfranchised any potential opposition to his rule within his family. Perhaps Louis's greed and poor morals influenced his own sons to fight amongst each other, dissolving the empire's unity and thus its integrity.
In summary, Louis was destined for problems with his empire's succession because he had multiple heirs and also because he espoused greed and singular authority. His father, Charlemagne, never had such problems, as he had only Louis as his heir and likely would have sought a united confederacy between his heirs, had they survived.