The authors of both the books, and the article act like they have no idea why the books would be banned. Amazon isn't out banning books from conservative authors just because they're conservative. There are thousands of such books and authors still being sold on the website.

I haven't read his books and I don't know why Amazon pulled them from it's website, but he is quoted as advocating for the legalization of rape as well as admitting to raping two women. So, maybe the fact that his books probably contain similar sentiments of advocating and promoting rape has something to do with it.