Because Governance and Statecraft are difficult, and need every day tools. The Theory and rhethoric miss lot of nuance and complexity of the situation. I am happy that a Politician once becomes president changes some if not many of their policies. Yes, there is an element of accumulation of power in some instances, but over all, the forces are much larger than one person or one team. That is why I find all the election promises esp. during the primary phase to be so funny, and incredible.
I find it interesting that, as detailed in this article, Obama viewed his decision not to attack Syria as breaking with "the Washington playbook"; yet in the subject article of this thread, Obama is clearly playing straight out of "the Washington playbook" in supporting the government's ability to invade citizens' privacy.
I think Obama said it wonderfully in this article http://www.theatlantic.com/magazine/archive/2016/04/the-obam... , No President starts with a Clean slate.