common example:
DVC Joe trades out 500 pts for a cruise. DVC makes a deal with the cruise line to pay for Joe's cruise, but needs cash to pay off the cruise division. DVC takes the 500 pts and books DVC rooms with those pts and offers them for rent through CRO (the wdw site, as you call it).
so in that case, those rooms are already being paid for with pts. and that is why you cannot book them AGAIN with pts.