I have noticed that Amazon (and Amazon merchants) seem to be unprepared for this holiday season. Amazon was always my go-to place for "oh shit I need a Christmas present at it's December 20th". I went online to buy a few things this weekend and almost every item I looked up was marked "Back in stock on Dec XX" where XX was somewhere in the range of 24th to 30th. So I'm not surprised that this extends to Amazon's own…
Current numbers, especially in the US, look very promising. Growth isn't where it has been in the past, but employment is very strong and so is spending. Wage growth will have a large effect on spending for gifts, especially for earners with low wages.
Maybe that's why Amazon was so surprised this year. They anticipated their growth number to what they sold last year and didn't account for the extra boost.
Of course that's just speculation, but it would fit well. And would explain why I don't see this effect on Amazon UK at all.