We know that Amazon, among other giants like Facebook, is exploring blockchain technology. When crypto is becoming more mainstream and when Bitcoin becomes more mature we can begin to hope that companies like Amazon will start accepting Bitcoin payments, maybe now, adoption is not safe enough for e-commerce giants, and this is to protect their customers.
I am certain that amazon and other E commerce sites will start accepting bitcoin eventually because it opens up international trading with ease without any headache of cash backs for the merchants and bitcoin is the only answer to get rid of the charge back headaches and other disputes in the future, if i am speculating, the main reason i think for getting delayed is that bitcoin still needs to scale for much bigger transactions for them to accept it and the volatile transactions charges might be the reason and once lightning network is adopted, then they might open a channel and start accepting bitcoin. 