My answer would be, “Because everybody lies.” Jack Shafer writes for Reuters:
The great fact-checking crusade of 2012 by FactCheck.org, PolitiFact, The Fact Checker, CNN Fact Check, AP Fact Check, etc. has told us something very important about the workings of democracy that we already knew: Candidates bend the truth, distort the facts, fudge the numbers, deceive, delude, hoodwink, equivocate, misrepresent, and, yes, lie, as a matter of course.
Both major-party presidential candidates and their campaigns routinely lie, as a Time magazine cover story recently documented, although the publication gave Mitt Romney’s campaign top honors for lying more frequently and more brazenly. Time is not alone in its assessment: Romney also leads Barack Obama in the Washington Post‘s Fact Checker “Pinocchio” sweepstakes. But the lies will continue until Nov. 6, after which the chief mission left to the checkers will be to determine whether the winner was a bigger liar than the loser.
The candidates lie about each other, they lie about themselves, they lie about issues they know intimately, and they lie about issues they barely understand. Of Romney, the Washington Post‘s Dana Milbank writes today that the candidate has changed, reversed and obliterated his views so many times that “Whatever Romney’s positions were, they are no longer.”
If either presidential candidate met you, he’d tell you a lie within 15 seconds of shaking your hand, and if he knew he were going to meet your mother, he’d invent a special set of lies for her. Politicians lie not because they’re wicked – though some are – but because they’ve learned that political markets rarely reward honest campaigners. Say what you will about Ralph Nader and H. Ross Perot, but they ran relatively honest campaigns on the issues, and the voters rejected them. The political market spoke many years ago and continues to speak: Telling the truth is not great for campaigns – and if it were, more people would be doing it…
Read more here.