That's a good question. What's their incentive to declare inventory? What makes Disney more money, declared rooms available for DVC Members or non-declared rooms available for CRO?
My understanding is that they can only sell units that have been declared into DVC.
I would assume that they have a certain # of units they use as a base and when the availability for sale falls below this base, they declare more units to keep up with sales.
I think I read somewhere (and can't remember where) that they started out with declaring 20% of the units.