Does Amazon hope that this investment in EV's and EV infrastructure will put them in a good position to sell EV's at some future point?
Maybe it'll give them a few years of de-facto monopoly in some cities/states that pass laws requiring all deliveries be carbon free?
Maybe being top of 'low carbon' company lists alone is worth it if that means they attract environmental conscious shareholders?
Maybe this is cheap positive PR which is cheaper than just spending an equivalent amount on adverts?
For a company so laser focussed on financial efficiency, the move to EV's doesn't seem to make a lot of sense.