The reason being because Administrative Agencies may only act within the power granted to them by Congress. Congress has the ability to delegate their power to the executive branch (which Administrative Agencies are a branch of). Every delegation of power has been upheld since 1937 (they cannot delegate power exclusive to Congress, such as the power to declare war, or to impeach). However, to delegate power, the legislative branch must provide the agencies with an "intelligible principle" on which they are to exercise the power delegated to them. Whitman v. American Trucking Associations, 531 U.S. 457 (2001)
In other words, they are not free to "strategically plan" only exercise the authority delegated to them by Congress by means of the intelligible principle. However, the intelligible principle may very well call for the agency to use their discretion in executing the delegation, which would permit the strategic planning which you are referring.