Easy. Because Afghanistan is the default choice in your form. I went to your form. And I found it with Afghanistan selected. If I were registering on your site without caring much about it, I would probably leave the Afghanistan choice, although I am not in Asia.
Are you sure you need the country ? Why not making this choice optional ? Are you sure you have put in the list all the countries the users may be in ? Have you put South Sudan ? Have you put Palestine ? Do you think a user from an “unrecognized” country, say Western Sahara, will be OK to choose Morocco because you forgot to include this user's country in your list ? Have you thought of putting the choice “Other” ? What if I am in French Guiana ? In your list, there are French Guiana and France, but I cannot choose both. In your list, you have many errors like this. You have two Iran, four Korea.
All geopolitics questions of the world don't fall on your shoulders. But if you make a country choice mandatory, you have to deal with them. If this choice is optional, it is less of a problem.
The sentence “Please tell us where you live so we can show you books that are available to you” makes me think of another problem. Many Web sites ask for the user's country although they don't need it. When I am quickly overcoming a registration barrier on a site, I often put a phoney country in this case. Worse : some Web sites, like Google and YouTube, use the country to make the user feel “at home” — so they think —, and filter content to show only the content “for” the country. On the World Wide Web, this practice is very bad. This is even contrary to the Web standard invented by Tim Berners-Lee. A URL gives a resource, and the resource is not supposed to be tweaked depending on where the request comes from. Your book sentence may mean you intend to do that. When confronted to a site doing that, users remove their trust, and they cheat. Don't forget that a user in Belgium may be interested in books available in France. Most people don't live in a bubble.
If you want to encourage your users to fill in the country choice, I have a suggestion for you. Ask them to pin their location on a world map. Some sites do that now. This is fun, and has more user engagement that a long country list.