Quick look at the cast and it looks like a bunch of non-Italians in starring roles. That’s like casting Ben Affleck as Michael Corleone.
The studio wanted Robert Redford as Michael Corleone. Coppola wanted John Cassavetes, who the studio thought to be too old. Coppola and the studio both wanted the Brit Lawrence Olivier as Don Vito (who would have been brilliant), but he turned them down and then we got the (non-Italian) Brando as a result.