Well that was unexpected. That happened really quick. They just got it in stock like 3 days ago. Must not have been a very big run. Yoda is now also waitlisted. I clearly waited too long
My guess—and this is purely a guess—is that both Sideshow and Hot Toys have been getting stuck with too much stock, due to people pre-ordering and then canceling.
Sideshow isn't just distributing Hot Toys figures, they are purchasing and reselling them. Sideshow takes all the pre-sale numbers and then pads that out a bit, so they have additional stock, once the figure eventually ships. So they may purchase 500 figures—based on pre-orders—and another 50–100 as stock to sell.
But over the past few years, it has become pretty obvious that Sideshow is getting stuck with a lot of unsold figures. It was probably always an issue, but I think the fact that Hot Toys has ramped up the total number of individual figures they release per year has had an effect as well. People pre-order all the cool figures that are being put up for order, but when when 10 ~$250 figures ship in a year, maybe more people are forced to cancel. Hot Toys shipping schedule has become a lot less predictable as well. A 1st quarter figure slips into 2nd quarter and suddenly a collector may have thee figures shipping in the same month, where they had planned for them to be a bit more spaced out, and are forced to cancel one or more of them.
My guess is that Sideshow is ordering less extra figures for stock. That way they lower the chances of getting stuck with unsold figures. They have also recently added the option (at least I only recently noticed it) to pay off your remaining balance on a figure whenever you want, before it ships. This would be another move that could lessen the amount of canceled pre-orders, by allowing customers to pay for figures on their own timeline, and not get surprised by random "Shipping Soon" notices.
So I think we may end up seeing more figures selling out, and selling out faster going forward.