CivLuvah
Deity
Simple, he is not Dutch and is and has never been never considered a great "Dutch" leader of the Netherlands.
Doing so would insult me greatly to be honest and I doubt Firaxis would do that. Ruling over a region as part of your empire doesn't make you a good choice as a leader for that civilization.
Willem even though born in Nassau, Germany was the face and leader of the dutch revolt against the Spanish.
It's like having Philip II for the Philippines. It not only makes no sense, as a Filipino it's almost insulting.