Their term of service says otherwise.
It’s very common with online digital content, so many language apps I use look nothing like what they started as, Duolingo, Lingodeer, Wanikani, Pimsluer. The only way to get unchangeable content is by buying a physical book/media, ‘cause when they change the content, it’s a new edition, and it doesn’t affect theway you use what you already bought.
When you buy an e book from amazon, it’s not really yours and can disappear from your library at any given moment. Idk who started this trend, but that’s the way it is.