I think one thing people tend to forget is that Disney isn't having an issue selling out Riviera via cash rentals so they probably don't care right now about selling out quickly, rooms go for a ton a night there and inventory is slim to none (again why Aulani as a failure for
DVC isn't as big of an issue for the company since Cash side is strong). The business model on Disney isn't only how quickly I can sell, but can I also keep renting via cash bookings, which in the short term probably has a higher ROI. Then if the market tanks, they will discount the direct purchases to stimulate sales in that market.
So I don't look at it as bad that the resort is selling out, Disney might have priced the resort to specifically keep the DVC sales at some level of interest (not 0) but also to keep enough cash inventory during a time when it is strong for them. Disney created DVC (particularly at exisiting resort conversion) to sell out rooms they couldn't via cash. But Riviera is special in that it is a new-build that I think is particularly popular for non-DVC folks too (though I think the echo chamber of disboards people don't aknowledge that it is very popular).
Also to their advantage not to sell out right now, when they can sell for cash, to delay until PVB2 comes online. The real bad would be for DVC to have no resort to sell at any given time, people buy on a whim for usage now. And interest would disappear if all the sudden their wasn't a resort to sell.
I'm also guessing the debt they took to build it is very low interest rate so better to hold onto that then sell (which triggers that debt to paid off) then to reinvest in new capital at higher debt rates.
Also these are January sales not February always been a complaint of mine since deed recordings take about 30 days.
TLDR: Riviera is a cash cow for Disney and they don't have an incentive to sell it right now.