John Saxon left out of The Godfather Triology

How is the recently deceased John Saxon, a standout in both Enter the Dragon and menacing Marlon Brando in The Appaloosa (1966) did not get cast in The Godfather Trilogy? John was an Italian American, born as Carmine Orrico to immigrant parents in Brooklyn in 1936 and was raised in the mean street celebrated by Mario Puzo. He studied with Stella Adler and gave some powerful performances. Close to the same time, film critic Roberto Curti referred to John's performance in the Italian crime drama as "a turgid, verbose and violent melodrama", in which the "only memorable asset is John Saxon’s over-the-top performance." He was as handsome as they come and would not have needed makeup to play Italian. Does anyone know why John wasn't cast, because he looks to have been a natural fit.