Because it's still entirely unclear what the arrangements for trade will be, despite the fact that the transition agreement ends on 31st December. For example,

Because it's still entirely unclear what the arrangements for trade will be, despite the fact that the transition agreement ends on 31st December. For example, the UK government are planning a number of huge lorry parks near the English Channel crossings to deal with new customs arrangements, whatever they may be, but they've only bought one location so far: https://www.theguardian.com/politics/2020/jul/12/local-anger-over-plans-for-post-brexit-lorry-park-at-ashford https://www.theguardian.com/politics/2020/jul/12/local-anger... Edit: to be clearer about what my point is, Amazon relies enormously on friction-free shipping. It might make more sense for them to plan not to ship across a border for a while until it becomes clear what the logistics will be of shipping across that border, rather than guessing what it will be like and getting it horribly wrong. The possible outcomes range from a decent free-trade agreement with minimal disruption (although that seems vanishingly unlikely now) to a hard Brexit (i.e. no agreement) and an immediate sharp stop to frictionless cross-border trade.