Why is there a need for strong political parties in a democratic system of government?

A democratic system presupposes the presence of many political opinions and views. And although in such countries there may be a large number of parties, 2-3 political associations usually play the main role. This is necessary for the normal existence of the system. After all, many weak parties will simply be unable to govern the state, and during the elections there will be problems with determining a single leader. That is why in democracies the choice (as, for example, in the United States) occurs between one of two large organizations.