you have (or your distro has) installed the widevine drm plugins for firefox (or whatever browser) that are included by default on windows and mac os. these are proprietary plugins, but some convenience-oriented distros distros include them because many users expect them.
some linux users are on linux because they want to eliminate proprietary software from their computer altogether. which means no access to un-broken drm media.
Everything and anything it possible on linux. The question is whether I want to bother. I could probably disable my browser's security features and get it working, install some proprietary whatever, but it isn't worth than hassle imho. I've got better stuff to watch than netflix/amazon junk. Whenever I have a hour to kill my first choice tends to be the BBC.
I think it depends on how mainstream your distro is, or maybe on what browser you use. When I used Linux, every streaming platform ever told me that my browser wasn't compatible to stream.
