If you own a Kindle, you can check-out books for free and not have to go to a library. There are only 5000 titles available and no publishers are on board, but if you are a Prime member, the service is yours to use.
The last time books were offered for free, people weren’t very happy. The difference here, perhaps, is that a cut of Prime subscription fees goes to the publishers, in some way. Unlike Apple, Amazon often prices the books significantly under value to drive people to the hardware and the ecosystem. Now, they are choosing to price some books for free (albeit with caveats). But, they are still “within the law”, so to speak, since they own the books to the extent that they can distribute them at any price they wish.