It's permanently blocked to prevent piracy, or something, mumble, mumble...
The temporary nature of any licensing deals behind these services and the resulting lack of reliable long-term access to content have become more and more obvious.
Increasingly the streaming services seem to be so paranoid about piracy that they are blocking "unapproved" players from getting the highest quality versions of the content - as if anyone who wants to pirate any blockbuster movie can't already find a way to get it in 4K somewhere else if they really want to. Meanwhile you can't watch your 4K movie on a service you're literally paying to provide that movie. IIRC Amazon Prime Video still won't even let you have HD content if you're on Linux.
It feels like the commercial incentives for tech firms to create walled gardens and a culture of never owning anything permanently are going largely unchecked and by now the governments who are supposed to act in the interests of their people should really be stepping in with regulation to counter those negative trends.