Why the US Blocked the Appointment of Okonjo Iweala

The United States happens to be the only one not in support of the appointment of Okonjo Iweala as the New Director General of the World Trade Organisation.

The given reason behind this by Robert Lighthizer, the U.S. trade representative was that he
perceived that Okonjo-Iweala is being too close to pro-trade internationalists like a former USTR president of the world bank , Robert Zoellick, who Okonjo worked with.

Well, i don’t think this is a tangible reason not to back her and there might be another reasons behind it, but it doesn’t really matter anymore because she emerged as the winner and now the first female Director General of the World Trade Organisation.

But if they were truly other reasons behind the US not backing Iweala, what could it be?