Yeah it can be fairly common for ABDL companies to be out/low on stock this time of year.
Many of them will shut for a period over Christmas so they get a lot more and bigger orders from customers before they close down for a week so they sell out faster.
There is also the fact that many of their customers may also have time off work over the holiday period where they are able and plan to wear more than usual so again customers order extra diapers in to make their holiday "special", as well as customers who maybe only buy ABDL diapers once or twice a year as a treat, using plain/medical diapers the rest of the time, buying themselves a "Christmas present" of fancy diapers means extra custom at this time of year.
Then there are stock and delivery delays as every single company that ships anything is trying to deliver more orders than usual meaning less space on trucks and ships and more difficulties for ABDL companies to get their stocks delivered, Also many ABDL companies may seem big but probably only have small and limited storage space for their supplies and so are unable to order extra amounts for this time of year to cover all the extra sales.
Couple all this with the fact that many of the ABDL companies will have just come out of black Friday and Christmas sales so customers have been buying more supplies/larger orders because it's cheaper and the store then has to replenish all that extra stock sold during sales.
There are probably a few other reasons too, so yeah they are often low at this point in the year.
