It is said that politicians lie because the public is wanted and likes to be lied to. The reason politicians lie is because people do not want to hear the truth. People do not like to hear bitter reality. People prefer to hear "what they want to hear", something that pleases their subjective feelings. When two candidates argue, one tells the truth and the other candidate says what the public wants to hear, strangely the candidate who says what the public wants to hear is winning the election.
Could it be that people expect too much? What do we expect from politicians? Should we expect moral perfection? Or should we expect them to do the work they are supposed to be doing? Political leaders are not kings who have absolute power and control over who lives and who dies. In the democratic era the political leaders we choose are not the same as the civil servants. We choose people to do the work. They work for us. They are our employees and we pay with people's money to generate people's welfare. But sometimes politicians lie because they "have to" do it. As political leaders they have to maneuver between all groups and individual pressures. They must be able to survive in maneuvers. Like a military general who can be a loser if he gives the right information to the enemy. The ancient reason, indeed, but still sells in a half-mad democracy.