Amazon could kill support for any platform at any time if they wish. If I get any eBooks at all I want them to be in an open standard (e.g ePub) with no DRM whatsoever.
And they have a history of doing this. Before they had the Kindle, they sold Adobe digital editions content, and after they made the switch they retired the Adobe digital edition license servers. I lost an ebook I desperately wanted when they did this. They didn't send a warning about the upcoming retirement either, despite the books being registered to email addresses which they could easily have sent alerts to.
They probably couldn’t do this to the kindle stuff now at this scale, if that’s any comfort.
I definitely prefer that. Amusingly, most of my DRM-free ebooks are in Apple Books, because it's become a really great reader and it's trivial to get "outside" books into it.
That is certainly true. But given the choice between Amazon or Apple when it comes to digital content I choose Amazon for the reasons given. Maybe they'll lock things down but I doubt it.
Bean books sells theirs on the kindle store with exactly that requirement.