A few months ago, SkyAuction pre-sold a lot of weeks and many people were posting here that they were thrilled to get this great deal. Perhaps, they've been taking their vacations and it's used up some of the excess inventory.
Also, in the last 4-6 months, RCI has a new link on their website where both Members and Non-Members can look to see what the general availability is like for rentals, Member Extra Vacations and other options. They've gotten better at marketing their rental inventory.
These, in addition to reasons described above, may have led to a reduction in availability.