Answer:
To have their interests represented
Step-by-step explanation:
In fact, and more directly, people elect politicians because they believe that the politician will do something aligned with what they believe to be the best course of action to achieve his own goals.
A person might be an ideological activist who believes in communism for whatever reason and it might cause him to vote in a socialist candidate because it is the closest that he will get from what he wants.
Someone who believes that government control, expansion, and communism are evil things might vote for a republican because it is the closest that they will get from a classic liberal type of economy.