I don't think Amazon want ebook subscription service to take off, but its hand was forced.
Apple/Itunes didn't want a music subscription service either.
Amazon doesn't want to be like Apple in that regard (way too late into the game).
Either way, customers are the BIG WINNERS in this regard.
http://www.forbes.com/sites/jeremygr...iption-market/
When Amazon Acts Like A Start-up: Why Amazon Has Entered The Ebook Subscription Market
In fact, Kindle Unlimited competes not only with Scribd and Oyster, but also it competes with Amazon’s more traditional retail ebook offering through its Kindle platform. Why would Amazon create a service that so directly competes with its main ebook offering? Why would it want its heavy readers, who may spend hundreds of dollars a month on ebooks through its Kindle platform to instead transition to paying $9.99 for much of the same?
Because Amazon is acting like the start-ups that are trying to disintermediate it. Scribd and Oyster are billed within the industry and to publishers as alternatives to Amazon, new ways they can reach readers without ceding more ebook market share to Amazon. If the strategy should prove successful, Amazon would lose buy-one-get-one ebook business to the subscription model anyway, but it won’t be reaping the rewards of such a transition. If the company launches its own version of an ebook subscription service, it can head off the disintermediators and reap some of the rewards of the transition to subscription consumption, taking a page out of this oft-reference start-up playbook.
Should the model take off and users read more ebooks the same way they watch movies and shows on Netflix and listen to music on Spotify, then it will be a horse race between the leading services — and Amazon wants to make sure it has a thoroughbred in the field.
p.s. Now that Amazon has enter the fray, it won't be long before Google, Apple will have one too.