But honestly, Audible is how I listen to audiobooks. If it's not there, I'm not going to buy it. I've pretty much transitioned all of my casual, entertainment reading to audio (still using physical/digital for more technical reading).
Of all companies, I think Audible treats its customers well.
The only reason I can think of for why an ereader wouldn't at least support importing from an open standard is so Amazon can make sure that you'll never buy books from anyone else.
FWIW, it bothers me, but largely for pragmatic reasons: Unless I routinely delete the automatically converted .mobi files, the size of my ebook library would more than double (.epub files are somewhat smaller than .mobi).
The practical difference between regularly syncing and backing up a multi-Gigabyte library and one that has twice as many files and is >2x larger is pretty significant.
And since I'm not keeping the .mobi files around, the conversion has to be done again every time I copy the book to my Kindle (for example, to re-read it), and the extra delay, particularly when transferring several ebooks, is rather annoying.
Looking at the reviews for the book on Audible, I'm not seeing anyone complaining about a shortened recording.
That sounds like a sample of the book.
It is absolutely frictionless and cheaper than competing services.
All my titles are available on all my devices, and progress syncs perfectly.
As a consumer, it is far far easier and more convenient than having to manually download mp3s off a shared drive or something, never mind the issue of how you sync progress.
It doesn't abuse me. It makes my life net better than it was before I used it.
This is a really important point for you - many people value what they practically get from a service - not abstract concepts of freedom.
What I care about is getting to listen to the book. I don't care about your DRM problems. I don't care about file formats. I care about the words that the author wrote going into my head. That's what I came for. If they give me that I'm a happy customer.