Are you familiar with self-published authors on Amazon KDP (Kindle Direct publishing)?
One of the first ways that self-published authors sell their ebooks is to other self-published authors. Why do they do that? Well, if you're writing in a genre, you want to read the latest stuff in the genre to keep up with trends, the best way to do that is to buy the ebooks of your fellow authors.
Once you generate a few dozen sales to other authors, the Amazon algorithms bump your books up in search, so they become visible more to the general public searching for books in that category.
You can think of it as author4author or buy4buy.
There are some similarities, but of course difference too, in author/viewer/creator and algorithmic behaviors.
Just my 2 cents worth. Take out of it what you will.