I would think that DVC is using some type of rational model that considers:
- their inventory (why buy OKW or VB points if you have a big inventory at a given time),
- demand (related to inventory, but also to any waiting list they have),
- use year (some potential customers want a specific use year, based on when they are likely to reserve, so they can cancel without penalty, if necessary; or to align with an existing contract for ease of point management),
- profit margin (selling price less total cost to DVC {cost / point, recording / transfer fees, dues, etc}).
- status of banked, current year, and borrowed points (DVC needs to bring contracts to a full current year available state to sell, and thus may welcome banked points, but has a cost to use developer inventory to replace borrowed points).
Such a model would drive different behaviors based on inventory and demand.