Or maybe because he’s the main character and not in a supporting role. And should Brando win over him he wants lose properly, nominated in the same category as him (the Godfather has 2 main characters). Instead of moving down to the supporting category, taking a supporting actor who deserved to win’s Oscar, taking a different actor’s nomination, and for the rest of time everyone thinking “Wow, did Pacino really move categories just to not lose to Brando and win one for himself…. what a bitch.”