Because the President needs to use mass media to obtain support for policies.
The executive office of the president includes press and communications staff in order to gain support for the policies. Mass media is very important since its goal is to inform the public and convince people of the importance of certain policies. Also, the president uses mass media to speak to people anywhere around the world.
Black nationalism, or "Black Power" as it is sometimes known focused on black people improving their own communities, rather than fighting for full integration into American society as a whole.