Why was it difficult for the king to do without the support of the knights and townspeople?

The knights were the elite of the state. Many of them had huge plots of land and were richer than the king. The king needed to enlist their support in order to have the support of his power in the person of the knights and exclude the possibility of a coup d’etat. The fighting efficiency of the army also depended on their loyalty, since the knights went on a campaign themselves and gathered with them detachments of infantry and cavalry.
The townspeople, along with the peasants, constituted the basis of the economic life of the state. The more the people loved their king, the easier it was for him to collect taxes and impose emergency duties. The cities were the center of life in Europe at that time.