Why do citizens choose a representative to vote for laws?
Citizens choose a representative to vote for laws because to do that is easier than to be a direct democracy like it was back in ancient Greece.
Citizens elect leaders who vote on the issues in a representative democracy, and citizens vote on the issues in a direct democracy. A representative democracy is modern, and a direct democracy is ancient. A representative democracy works better in large groups, and a direct democracy works better in small groups. Citizens' desires are ignored in a representative democracy, and citizens' desires have a better chance of being heard in a direct democracy