Long political habit of presuming that things said on the campaign trail will not be remembered by the media. We've only had tiny portable movie cameras in the hands of practically everyone for a few years- ditto the ability to instantly distribute the resulting video around the world.

For centuries politicians presented different faces to different people, confident that they couldn't/wouldn't compare notes and that the media would never know. That era is over, but the habits persist... and all too often, the "official" mass media perpetuates it, because they don't want to lose their precious "access" to those politicians.