The Pulitzer prize-winning PolitiFact is run by the Tampa Bay Times, and its reporters and editors sort politicians' claims into one of six categories: true, mostly true, half true, mostly false, false, and pants on fire — the last having an element of the "ridiculous... This month, 60 percent of Republican claims have been rated as lies, while 29 percent of Democratic claims have been."
See charts here...
http://www.theatlanticwire.com/politics/2013/05/politifact-lies-republicans-vs-democrats/65688/
Why is that? It's possible the fact-checkers are intentionally or unintentionally letting some bias show through. Whether or not that's true, the state of each party right now most certainly plays a role. A lot of very conservative Republicans got elected in 2010, and the Tea Party got a lot of attention, and some Tea Party Republicans have had a tendency to say inflammatory things. Like, say, Michele Bachmann...
Why do cons lie so much? Because they are shills for and represent the interests of big business. Whether it's big business interests inside our country or foreign interests, the right knows their butter is not on the side of the people. Like Anti-Party said..."Everything they say is Corporate driven."
Right wing politicians are not about governing and making this country strong and healthy, they're about getting as much personal wealth as possible using their positions. They've proven over and over that they will lie for corporate money. The funny thing is... there are idiots who work for a living that believe their lies, lock, stock and barrel.
From trickle down, to 'the war in Iraq will pay for itself', to aluminum tubes from Africa, to the insanity of Bachmann, its all about someone on the right selling snake oil and nothing more.
More simply, why do they lie? Because they can't win elections (and get rich) if they tell the truth.