Not even Amazon forces publishers to use it! There are DRM-free Kindle books available.
Unfortunately, I don't know of a way to explicitly search for DRM-free titles, but the description for these usually has a sentence like "made available DRM-free at the publisher's request", or is lacking the reference to "use limited to x devices simultaneously".
This is why I not only favor purchasing DRM-free media, but also keep a local archive of all such purchases.
$ ls /mnt/comixology | wc -l
239
(This can be a bit difficult for larger‐sized media, such as video games, but I do it anyway—my GOG archive is over two terabytes.)
I also have a small collection of DRM‐free music I had purchased and downloaded from Amazon that no longer seems to be accessible online. Certainly I have no plans to purchase anything digital from them in the future.
Including in KDP. There's a tickbox for whether you want DRM or not. Personally I'd never add DRM to mine because it's so trivial to strip anyway and just an inconvenience.
If Amazon doesn't demand it, then it must be the book publishers that are actually demanding it. So it's not just big bad Amazon after all. That's interesting.
Unfortunately, I don't know of a way to explicitly search for DRM-free titles, but the description for these usually has a sentence like "made available DRM-free at the publisher's request", or is lacking the reference to "use limited to x devices simultaneously".