Assume that the money they have to devote to "improving the
DVC margin" is limited, and they are committing all of it. Would you rather ROFR something that you can resell quickly and for which you don't have ready inventory, or would you rather take back a subsidized Aulani contract when you already have a pile of unsold Aulani points?
Even though it makes sense to buy it back, there might be more profitable ways to use that money. I also suspect that the total set of subsidized points is small enough that the cost never rises to the point of being noticed relative to other costs in the system.