Because for inventory at resorts that are not declared, DVD can sell the points to Disney to use for cash reservations. And if a DVC member makes an exchange, the "room" is sold for cash on the Disney website to pay for the exchange. This has come up many times here in the past. The rooms come from a completely separate inventory. You can Google for a more in-depth explanation.
In addition to points not declared into the condominium and points available to DVC because the owner exchanged them for a cruise or deposited them to Interval International, by Florida timeshare law DVD must retain ownership of a minimum of 2% of points at each resort, to allow for taking villas out of service for repairs or maintenance. At any given time, DVD owns more than that due to foreclosures and other reasons. DVC, like any other owner, is allowed to rent their points, and they do that by listing them on the Disney website for cash reservations. In addition, any villas not booked by owners by 60 days before checkin can also be given to Disney to rent for cash. So, as above, the villas you see in DCR come from a completely different inventory from what's available to owners.