As you have seen that more and more users from India are now getting into crypto currency and companies like zebpay and coinsecure makes it easier to buy bitcoins.
So do you think merchants like flipkart and amazon should use bitcoin as alternate payment gateway.
If course they should accept bitcoin payment also but the question is why would they do this?they are the leaders in their niche and they wont see any additional advantage of using bitcoin payment gateway.Remember most of Indians prefer COD payment option anyway.Adding one more option would increase their business.Nobody is holding their purchase from these sites because they dont have option to pay with bitcoin