On December 1, 1946, Miguel Alemán Valdés became president of Mexico. He was a civilian and a law graduate of UNAM. According to México Desconocido, official protocol used his academic degree “como título de su investidura” (as the title of his office).
Many politicians then began to use licenciado as a title of prestige. Mi licenciado became “sinónimo de poder” (a synonym for power) in politics, the law and the bureaucracy. From there the use spread to the rest of society.