What was the weakness of royal power in France in the 9th to 11th centuries?

In the era of fragmentation in France from the 9th to the 11th century inclusive, royal power was very weak. In 877, Charles signed a document according to which the estates of the deceased vassals of the monarch were inherited if the son served with the army of the king. In France, with the weak power of the Carolingian dynasty, there was an unspoken law: the vassal of my vassal is not my vassal. The kingdom was fragmented into a dozen small and large regions, headed by dukes and earls. The monarch had full power only in his royal domain – Ile-de-France. Provence, Gascony, Brittany, Normandy, Burgundy not only did not obey the king, but were often his opponents and adversaries. After the death of the last Carolingian in 987, Hugo Capet, the first among equals, was elected to the royal throne.