Source: Self-Publishing Advice
While having all your books available exclusively from Amazon has its perks, there are also many benefits to “going wide” with your catalog of books.
From the original article:
“Here are some of the top reasons to use an Amazon alternative book sales channels:
Keep more of your profits. Many alternatives give a higher percentage of each sale to the writer.
Build a loyal audience and generate a mailing list. You can leverage the mailing list when you create a new book or promotion.
Sell from your existing channels, like social media and your website.”
There are many other reasons listed included in this in-depth article which includes breakdowns of other potential book outlets for both print and digital books.