At that time, Brazil was in the peak of a military dictatorship, and the Brazilian Armed Forces were unwilling to allow even their civilian supporters to have any real share of power.
The three junta members announced that Costa e Silva was gravely ill, and that the High Command of the Armed Forces considered that the domestic situation (especially in view of the recess of the National Congress and other measures imposed by AI-5) was incompatible with the transfer of executive authority to a civilian.
Also, the physicians attending the incapacitated President were of the opinion that he would never recover from the physical and mental consequences of the stroke and that accordingly he would never be able to resume the powers and duties of the office.
It was also claimed that during intervals of lucidity, Costa e Silva had told military personnel and members of his family that he desired to be replaced president.
In reality, the role of the Legislature (which had been purged of several opposition members under the provisions of AI-5) was merely to rubber-stamp the names chosen by the military elites that controlled the regime.
Thus, the representative of the Navy was always mentioned first, followed by that of the Army, and then by that of the Air Force, which led some to believe that Admiral Rademaker was first among equals in the workings of the Junta.