As a reader, you may or may not know how books are made available to borrow for Amazon Prime members and those who subscribe to Amazon Unlimited. Many big-name publishers get special access through special deals, because they're special. We indie authors (and those published through small presses) who distribute through Amazon's KDP program are given the option to participate by way of what's called Amazon Select.
Opting into Amazon Select requires exclusivity to Amazon. That is, authors who put their books into Select cannot also sell them at Barnes & Noble, Kobo, iTunes, or any other retailer. If books are selling at other retailers, it's a huge risk to pull them out and hand over the keys to Amazon.
I've tried Amazon Select because, let's face it, I have to eat. I have a mortgage to pay, an electric bill to power the computer with which I write books, internet bill, phone bill... in other words, I'm a person without a deep pocketed spouse to pay my way through life. 100% of my income is through my writing, and sometimes that income is less than what I need to pay all the bills.
Generally speaking, I want my books to be available to anyone who wants to read them. I want to log into my account at Nook Press or iTunes or Kobo and see people buying them and enjoying them and wanting more! But... that's really only happening for my Kinshield series. It's my bread and butter, so I probably won't try Select for that series again (unless the exclusivity requirement is lifted).
The Mindstream series, on the other hand, is not getting much traction at other locations. So far, for the month of June, I've sold six copies of those books outside of Amazon. SIX. I can't live on that! And so the Mindstream Chronicles will be removed from sale at all retailers except Amazon so that I can try them in Select until the end of July.
You see, Amazon is making a change to the way authors are paid for borrows in the Select program. Rather than pay all authors the same for each book borrowed, they're going to pay for each page read. This means that authors of epic sagas who hold a reader's attention will earn more than someone who puts up a 2500-word short story. That's great for writers of sagas, assuming the work is compelling enough to hold the readers' attention.
If participation in the Select program still turns out to be a dud for me, I'll opt back out at the end of July and return the books to the other stores. It's not that I want to give non-Kindle readers the big middle finger. It's more that I need food in my belly if I'm to continue writing full time and not have to go back to a 9-5 job. :)