I also think part of the lack of supply is they are mostly closed over the extended break so the stock listed on the sites are only going one way.
From a business point of view, it's a lot easier to automate sales of existing stock you know for certain is there (until pre Christmas stock runs out) but if you aren't open then it's harder to replenish your stock on hand.
If product continues to be unavailable past Jan 5, then that will be indicative of a real supply problem (IMO).