The 'ol Firefighter is correct as usual!
VB is not yet sold out (neither is HH), but is approaching 75% sold. The developer does have more availability at these resorts than at OKW and BWV. At some times of the year (usually winter months at VB) the rooms do get reserved quickly. In this case, the developer rooms may already be reserved and any further availability would have to come from unused member inventory.
Another possibilty is that since VB is having an increase in sales activity, the developer has declared more rooms into member inventory for use in anticipation of more sales- so the result is the same- no current cash availability at VB. This certainly occurs at HH in the summer also.