The people are making that choice, as the party is an organization of the people who vote within the part for what the party stands for. Because there are many political parties, a party is more of a set of ideals, rather than a group of people who practically agree on nothing (like in the U.S.). Also, because there is voting within a party, it means that the representatives chosen by the party actually fit a set of specific ideas (not a garbled mess of arguing and infighting like in the two-party system). A party should be a unified group that pushes one idea.