Hi Reba, I won't repeat what the previous person said about author's (but that is true). What you can do to get more books for free is to link up with your local library. They offer many ebooks that you can view on your Kindle.
The authors need to make money on their work. They make money by selling the books. Some authors offer the first or second book in a series for free so that readers will see what their work is like and will want to read more. There is a new program through amazon where books are free through a membership similar to prime (or maybe it's an extension of prime?) There are MANY free books though and sometimes a book will only be free for a day but if you get it that day it's yours. The publishers are usually the ones responsible for making the books free. Happy reading!