Theory? Try common knowledge. Giancana was the most well liked, well respected don of all time in Chicago, of course you'd have to take out everyone close to him before you go in for the lion kill, and those that can be persuaded you reward for betrayal. Really, they had to wait for Ricca to pass before killing Moe, that was the main thing. But DeStefano, Cain, etc weren't just flattened for no reason. DeStafano getting popped for being a media nut is bullshit, the Outfit didn't give a fuck about that, he was one of the most prolific, effective juice guys in the country. But he was loyal to Moe, and Aiuppa/Cerone knew that guys that were fiercely loyal to Moe would never comply with them/respect them. Giancana's passing was when Cicero via Joey Aiuppa regained power, and you had the beginning of the Aiuppa/Cerone era, with each crew being like its own separate, mini family, and the top crew being the one the boss belonged to.

PP I will go more into all of that in the Fratto topic a little bit later, I apologize for the delay.