Thanks for posting this, Irishman, I always appreciate serious, detailed analyses of Trilogy plot themes.

In this case, I think the answer is much simpler: Michael knew, almost immediately after the Tahoe attack, that Roth was behind it. Only two people--Pentangeli and Roth--could have benefited from killing Michael. Pentangeli was the obvious one because of his beef over the Rosato brothers and his desire to get Michael off his back. But, he was too obviously set up as the patsy for the shooting. The big prize was Havana, not three territories in the Bronx. As Pentangeli admitted to Michael in NY (and as Michael already knew), "I don't have your head for the big deals." Contrary to what this film says, Michael already knew it was Roth when he met with Pentangeli in NY--he said so to Pentangeli--and before all the play-acting Roth did in Havana. The only outstanding doubt was to find out who was the traitor in his family.

A long time ago I posted that greed blinds otherwise intelligent people to the obvious--and dangerous. Michael's greed for controlling all the legal gambling in Nevada and Havana blinded him to the obvious: Why would Roth sit still for Michael's killing of Roth's best friend, Moe Green? Why would Roth sit back and let Michael barge into Nevada gaming almost as soon as he returned from Sicily, and take over Klingman's holding in a hotel Roth part-owned? Why would Roth--if, as Michael said, thought he'd live forever--turn over all his Havana holdings to Michael? And why, especially, would Roth, who lived in Miami and had business interests in Nevada and Havana, involve himself in a penny-ante dispute over three territories in the Bronx?

Michael didn't see all of this before the Tahoe shooting because greed blinded him to the obvious. The bullets flying in his bedroom opened his eyes.