I think the problem comes from Aluani. People bought there but are staying in WDW. The other off-site resort, Vero Beach and Hilton Head, aren't very big so WDW could handle those people coming and and they could handle the owners from WDW. But Hawaii is so far away that owners from the WDW resorts aren't traveling there.
Have you ever researched availability at Aulani? Demand is VERY brisk at 7 months most of the year.
It's difficult to summarize because there are so many different views and room sizes--19 different categories. Right now only 5 of those categories have full week availability over the next 5 months. And that availability is all bunched around late-April / early-May.
Aulani does experience something of a lull in the fall. But spring, summer, and holiday periods in particular, rooms are filling at 7 months with many non-owners coming away disappointed that they can't get what they want.