There are a lot of first-time authors using Kindle to launch their novel. They decide that they're going the Kindle publishing route first, because traditional publishing is difficult to break into.
There are a lot of people trying to publish a book. They have great stories to tell and they write well. Yet, their manuscripts often end up at the bottom of the slush pile and never grab an editor's attention.
Why is that? Because when you try to get published the traditional way, you're trying to get a foot in the door at the same time as many thousands of other people.
So, the competition is pretty fierce. Not only that, editors can drop the ball. They bypass manuscripts that end up becoming best-selling novels because they make the wrong judgment call about the manuscript.
Many authors who have been overlooked with traditional publishing have found a great deal of success on Kindle - plus, the money is better. With traditional publishing, you only get a small portion of the proceeds.