Casually worth noting the obvious: There are also services like Libgen and Anna's archive that are completely DRM free and have pretty much anything you can get on Amazon except, well, for free, aside from also being DRM-free.
Genuinely, what is your motivation here? People often justify piracy in terms of their opposition to DRM, but here someone is showing you how to get DRM-free books, and your response is "But over here they are free." They clearly aren't meant to be free, and people put substantial amounts of work into creating them. Don't you care?
All of this aside from very reasonable arguments that copyright shouldn't apply to consumer uses of information.
I don't really share your moral views on piracy, so why both browbeating with them?