The publishers originally had a great system, back before the internet was alive and kicking - they'd sell the textbook in the USA for $bigbux, and sell the exact same one in India for $cheapasfree - basic standard price segmentation, charge what the market can bear in each market.

But then the internet and cheap shipping appeared, and suddenly people in the USA realized they could get the same textbook by ordering it from someone in India, and pay $cheapasfree + $shipping.

And ever since the publishers have been trying to get back to the original promised land.