It's probably because Widevine on Linux doesn't support VMP. But even Amazon Prime Video streams in SD on Linux, better than nothing but still a bad experience for users.
If you don't like DRM, why do you want to buy/rent Disney stuff from the company that invented and bribed Congress to create modern Draconian copyright law?
Yet you seem pretty annoyed by their lack of Linux support...
I don't want to go too far on this because I agree with you on DRM, but "doesn't work on Linux" is a non-issue for most consumer products, for whatever reason.
Sure, you should be annoyed, since it's caused by them using DRM ;) I pointed it out very explicitly in the original comment. I.e. it's not like they are specifically anti-Linux, they are simply DRM obsessed. Which of course doesn't make it any better for Linux users.
I think it's more that they are DRM obsessed and don't give two flying ducks about Linux. If Linux were important, their DRM would work on it. For one I blame them, for the other I don't.
I have to admit I just don't care that much anymore. In the spectrum of things I have the time and energy to really care about, DRM has fallen off the list. I want to watch The Mandalorian, and damn; it was pretty great.
My point is simple, DRM-free services have no issues with video on Linux, because video doesn't really depend on the platform. Video is video everywhere. As long as they aren't using some crazy custom codecs that no one has support for, it will work.
DRM on the other hand is a platform dependent junk. So quite naturally it limits use cases which work with it.
Well, they don't need to care (about supporting DRM), they just need to stop being DRM freaks to begin with and start releasing DRM-free. That's the only real fix :) But of course, it's Disney we are talking about. They never learn.