Maranzano was still boss and winner of the Castlemmare war. He already had Stefano Magaddino, Joe Bonanno, Joe Profaci who were loyalists during the war. Gaetano Gagliano who switched sides with Lucchese to Maranzano who was unsure of their loyalties but made Gagliano boss and Lucchese underboss to keep many of the Bronx and East Manhattan mobsters happy. Same reason he made Luciano boss and Genovese underboss to keep that family happy, and Maranzano did not want to give Luciano a strong ally as the war was just over, and Vincent Mangano was one of Maranzano loyalists during the war. So he demoted Frank Scalise and made Mangano boss of the Gambino crime family. Scalise went along with it cause now he was able to concentrate on earning and not worrying about the whole family.