Time zones may also be a factor. And Black Friday began as an American phenomena, which has been exported.
I was surprised how much it has been adopted up in LatAm. For example, you can pick any country on Mercado Libre's list[0] and they'll have Black Friday going. Not "Viernes Negro" either, but the actual words "Black Friday".
Other measures indicate similar concentration in roughly the same places (excl. maybe China), such as a light pollution (indicator of energy usage): https://www.lightpollutionmap.info/
China obviously, there's not much they wouldn't just buy on domestic platforms using domestic payment services, but almost all of Asia is pretty dark on Shopify, compared to your map. I guess they're just not a thing there, plus maybe black friday itself. Also, the UK is disproportionately brighter on the Shopify map compared to the rest of Europe. Interestingly, light pollution seems pretty low in Germany compared to the Netherlands, but in Shopify it seems to almost be the inverse.
Definitely a factor, but Japan and Hong Kong were going pretty strong compared to the rest, so there's at least that. Would've expected Taiwan to show up in a similar fashion, but also almost nothing there.
Probably the fact that Black Friday is an American phenomenon that is successfully exported to mainly Anglo countries. Doesn't impact mainland Europe as much.
I don't see how Brexit could be part of the reason. Unless the economy is so bad more people are determined to find a bargain.
There's more Black Friday marketing in Britain than some other European countries, and maybe more use of an American credit card based shopping platform.
There should be a something similar to Godwin's law but for any discussion about UK. The longer the thread the more likely someone will mention Brexit.
I was surprised how much it has been adopted up in LatAm. For example, you can pick any country on Mercado Libre's list[0] and they'll have Black Friday going. Not "Viernes Negro" either, but the actual words "Black Friday".
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[0] https://mercadolibre.com/