@gailcalled That’s probably because those are books not under coyright any more and are available to the lbirary for free. We are just starting to experiment with lending Kindles at my library.
Archive.org is a great site for audio books. They have hundreds, free. They also have thousands of old time radio dramas, also free. Both streaming and download.
It’s not the easiest site to browse, but if you look through it you’ll be amazed and impressed at what they have