IIRC, he didn't believe there should be a competition for an award. You have to remember this was in the early 70s when there was a lot of anti-establishment sentiment and the Academy was considered part of the establishment back then.
"Patton" is one of my favorite films, and one of the best bio's ever.
A testament to its greatness:
My ex-girlfriend, native Mexican. Anti-war, doesn't like action films very much, a decade younger than me so pre-80's films (especially in English) were totally "foreign" to her. But she was a Jerry Goldsmith fan and I was showing her the opening theme as an example. We ended up watching the whole film, and she liked it. I have a library of about 500 films and we watched quite a few together...and I'm always surprised that "Patton" is one of them.
By the way I was lucky to get the 2 disc edition, it had been out of print for a year but a Suncoast video had it hidden away in their "box set" section! (At the time 2 disc sets were fairly rare).