I can guarantee Bill's reason is because he wants the money he provides to be used as efficiently as possible. You want the most benefit to be provided for you

I can guarantee Bill's reason is because he wants the money he provides to be used as efficiently as possible. You want the most benefit to be provided for your dollar. You want to donate to the organization who can use your funds at 70% efficiency, and not one that will use it at 7% efficiency, otherwise you are providing less good for your dollar.