At least in Germany, using Amazon is often the easiest way to buy copies of foreign-language (often, but not always English) textbooks about scientific topics.
Perhaps the reason is that the scientific textbooks that I love to buy are often "long-tail business", i.e. textbooks about very specialized topics.
The situation is even more biased towards Amazon if we are talking about used obscure textbooks in good condition for a fair price.
At least in Germany, using Amazon is often the easiest way to buy copies of foreign-language (often, but not always English) textbooks about scientific topics.