Why aren't all my favorite audiobooks (found here) not on audible.com?
No, I don't volunteer to do it. :)
Audible.com already has answered your question here:
http://about.audible.com/contact-us/what-content-is-the-most-popular-with-audibles-members/
Podcasts and other “free” programs – We’ve had countless conversations with our customers on this topic. They have told us that they get frustrated when they find out that the content they buy at audible.com is available at no charge in other places on the Web. Many of our customers have even reviewed these books negatively for this reason; as you know, such reviews can show up in public search sites such as Google, Yahoo and others, and can be damaging to the author’s brand as well as to the publisher’s brand. Therefore, we think it is best for our customers and authors that we not sell content that is offered at no charge in other places.
Thank you for your reply.