This is the result of a recent law in California:
https://www.theverge.com/2024/9/26/24254922/california-digit...
https://www.theverge.com/2024/9/26/24254922/california-digit...
https://www.theverge.com/news/612898/amazon-removing-kindle-...
From the article you linked:
>The new law won’t apply to stores that offer “permanent offline” downloads
Amazon is actively choosing to do this to maintain an even tighter grip on their ecosystem