Right now, as mentioned, only 75% of the resort is declared for DVC so 25% of the rooms are still owned by "Disney". So, some of the rooms that you see are those owned by them--try to think of them as another owner who is advertising the rooms they have reserved.
Now, as owners of VGF begin to trade out of DVC for options like a
Disney cruise, etc., inventory equivalent to the points used are given to Disney to pay for trade--ie: if someone spends 200 points for a cruise, then 200 points worth of inventory is given so it can be booked with cash and the cash used to pay
Disney Cruise line. Which rooms and dates chosen for that is anyone's guess but its up to Disney.
And, at some point, if a DVC room is not reserved 60 days out, they can be given to Disney to rent and the income is put back into the DVC budget as 'breakage". Again, someone mentioned that Disney can anticipate this based on historical data. In some cases, when you are within 60 days of arrival, CM's have been able to recall these types of rooms back. IMO, the number of rooms going as breakage is not as high as things likes trades and Disney owned rooms.