Kindle Unlimited offers nothing from big presses, and no guarantee the authors will get paid fairly for their work. Libraries buy the book up front for a higher price (and a better binding). Kindle Unlimited offers the authors a variable percentage of a as-yet-undetermined-and-unannounced amount of money.
While Amazon touts Kindle Unlimited at “Netflix For Books!” the reality is Netflix signed contracts with everyone whose work they offer so that actors, screen writers, best boys, and the rest of those people get paid for the shows and movies you watch. Amazon does not.
That means your favorite author isn’t being compensated for their time or work. If you love a book series and want to see the next one get published: buy the book or hit the library. Starving authors quit writing because they like eating.