Some guys added notable comments, but do not want to post answer, I'll try to compilate their point of view, because it is valuable I think.
Gülen extradition have some close ties with U.S. interacting with pro-Gülen forces in Turkey. When there was a armored coup attempt some time ago, all European countries reacts in public only after 4-5 days, when uprising was vanished.
Erdogan is not very comfotable for U.S. as ally, because he have some tension with U.S. in kurdish and human rights question, so U.S. have this ace-in-the-hole, Gülen, in their pocket.
About "state court decision" - really, I do not understand if a court of state can really affect U.S. foreign politics. If these courts are really independent from goverment decisions, it is a very strange scheme of power, I think.