The cheap books are heavily browsed by readers. Amazon doesn't have to do more than provide the browsing features for people to find the new cheap novels. Self published novels don't sell well right away. The most successful self published authors build a brand. You want reviews on a novel that tell people the books are edited, proofread, and interesting.
Some of the successful ones are building series. Every time they release a new book they have new readers will go back and buy all of the past books in the series as well. An author might not see much money until they have three or more stories in the series published.
And if you turn successful at this, Amazon.com will start lobbying people who read books in that genre to read your books as well.
However you would need to do some side work to get your name out. You need people who are going to read your works and post positive, but honest, reviews. It is generally best to seek them out among friends, forums, and contacts who read the same genre of book.