J. Marshall Unger's Literacy and Script Reform in Occupation Japan goes into details on this.
There were kanji abolitionists and pro-kanji people in both the American and Japanese administrations, and it definitely wasn't just a popularity contest. Things happened such as one pro-roumaji principal who enthusiastically took part in roumaji feasibility experiments being assigned elsewhere because he was having results, or one American pro-kanji official decreeing that roumaji publications should be published in triplicate since there were three competing romanization systems - Nihon-shiki, Kunrei-shiki and Hepburn - so they wouldn't unduly advantage any particular romanization system.
This of course also just so happened to make roumaji publishing three times more expensive. Whether fairness or limiting roumaji publishing by financial means was the real motivation is left as an exercise to the reader.
There were kanji abolitionists and pro-kanji people in both the American and Japanese administrations, and it definitely wasn't just a popularity contest. Things happened such as one pro-roumaji principal who enthusiastically took part in roumaji feasibility experiments being assigned elsewhere because he was having results, or one American pro-kanji official decreeing that roumaji publications should be published in triplicate since there were three competing romanization systems - Nihon-shiki, Kunrei-shiki and Hepburn - so they wouldn't unduly advantage any particular romanization system.
This of course also just so happened to make roumaji publishing three times more expensive. Whether fairness or limiting roumaji publishing by financial means was the real motivation is left as an exercise to the reader.