Dirty Disney Secret - they hold back some of the timeshare units for cash reservations.
I just tried to book a OKW for a friend in June 2-6 and it was sold out to me using DVC points but is availbale for a cash reservtion.
When people book on the Disney cruise or a Disney hotel on points, Disney has to make up the cost somewhere, so those points are used to reserve DVC and then rented out for cash. If they couldn't do this, then they would have to remove the options for cruise and Disney hotels.
Don't think of it as a 'dirty secret'. It's more comparable to the Disney member booking a DVC room, then trading it to Disney for a cruise. Then Disney rents the room to recoup the cost of the cruise.
Additionally, as mentioned, Disney owns a small percentage of each resort.
And undeclared inventory (at SSR and AKV) is available for Disney to rent, but not available to members on points.