Eric:
Actually, Oregon put in land use zoning in the 1970's which designated certain areas as resort/recreational ... they are zoned for golf, but only if there is a certain percentage of accommodation for visitors. So, most people developing real estate and golf in these zones develop multiple courses -- one private, one public.
I'm not sure if that is the reason Pumpkin Ridge is the way it is, but it is certainly true of all the newer courses around Bend and also of Bandon Dunes, which like some others just stayed entirely public.