what made the AAU Mr America unique was also the reason it died a slow death. It was not just a bodybuilding contest. The winner was suppose to be the best representation of the American male. Besides physique, you were judged on other characteristics, including athletic ability in other sports, appearance, grooming, the ability to speak in public, etc. Because of that, the most muscular guy on stage rarely won.
in the 1960s, the IFBB said they are doing it differently, that they will judge only on physique. (too bad that later became only mass) The audience responded, and the IFBB took off and the AAU declined.