You may not know this, but the President of the United States doesn't have an office in the NSA, and doesn't have direct access to their leadership or decision-making.
So no, Obama isn't trying to achieve anything, as it is somebody else doing it.
Being able to fire the person at the top gives limited control in certain types of circumstances. In a regular business it means you have a lot of control over a department. But even a large corporation, you might not be able to succeed at getting things done the way you want just by firing department heads; and there is a cost to morale in attempting it.
In the case of Government, the workers are the same under one President and the next, and they can drag their feet and wait-out a President who tries to micro-manage them. But also, appointing department heads for a President is a political act, it has real cost, and if you try to do it with a weak hand then Congress will win that battle. Also, the departments have entrenched support from Congress-critters that have been in place longer than the President and will be in place after his terms expire.
You just can't use a small-business-owner model of Control to understand the powers of the President here. He's the one that has to explain the policies to the people, but in Intelligence and Law Enforcement, Congress has erected barriers to direct Presidential control. People often imagine that the President can just walk into any department and look at anything and order anybody around, but actually he's not a dictator, and can only move the levers of power that are provided.