Brando Was Putting Everyone On
I think Brando has achieved the status to some fans that anything he did was fine art.
In the context of Brando's great performances; "Streetcar", "Godfather", "Last Tango", etc., this performance is the equivalent of Brando passing gas on film and all his fans reacting as if it was genius.
I read once that the Picasso was at an exclusive restaurant with friends and someone asked him what was it like to be Picasso. Picasso replied by drawing a few doodles on a napkin and paying for the dinner with it.
Brando grew to hate Hollywood and frequently did his best to show his contempt for the whole movie making process.