Why do politicians simplify statistics?

Answer 1

Because people usually aren't clever enough to follow along precisely unless everything is made as clear as possible. That means saying things like "62% of drunk drivers" instead of "a mean of 61.63% of drivers with BAC above the legal limit in several studies" and "10% increase" instead of "9.82% above the limit from the period July to December".

There's also a thing called spin-doctoring; making stuff sound as good as possible for your own side, or equivalently as bad as possible for any other side. Statistics, when simplified, can be misquoted very well and are perfect for being doctored in this fashion.