Kindle Direct Publishing (KDP) is a print-on-demand platform for self-publishing authors, formerly named CreateSpace. It is driven by Amazon, Inc.
Many authors use self-publishing platforms today, which doesn't basically mean their publications are not as good as those published by a publishing company.
The Wikipedia e.g. doesn't like references to self-publishing platforms, but IntactiWiki uses these self-publishing platform references, too. The reason is that many publications on the topics of genital mutilation on minors will never find a publisher company just because of the topic. Some of them may fear the anti-Semitism club, others may just not want to spread the word about this issue, especially in the USA. While it is quite normal that authors may have to spend years for finding a publisher, protecting children from harm has no years to wait. Therefore, more and more intactivism authors chose self-publishing platforms.
The readers always have to judge themselves whether information given in publications are serious or not. Chances are that publishing companies accept less unserious content than self-publishing platforms which also do some kind of content control. But there's no guarantee that company-published books are even more serious or reviewed than self-published works. Judge yourself, please.