For a long time this was quite a list. Through the years the number of ski areas which prohibited snowboarding has diminished steadily. This was imminent given the continued strong growth of the sport. Ironically, there may actually be more inbound terrain open to boarders this year than is open to skiers given the number of snowboard parks and pipes which are closed to skiers.
For any number of reasons a minority of resorts do not allow boarders and some probably never will. The number in the USA, now at 4 with full prohibition, has been shrinking steadily. They are:-
If anyone knows of any resorts outside the USA that bans boarding, please
let me know. I'll be staggered.