The primary role of the World Bank is reducing poverty and tackling health and development issues by lending money to spur development of national structures and institutions.
I don't think you need a banker for the job. I do think you need someone that is familiar with negotiating with foreign governments, combating corruption, and making sure money is spent developing national infrastructure and government programs that in turn address the issues of poverty, malnutrition, disease, etc.
Mr. Kim has very admirable and commendable background but it is not a great fit with the skills needed to tackle the wide variety of issues that the World Bank President is expected to tackle.
That is why I think it is an odd choice.