This is about how a writer understands and knows the bitcoin journey process and maybe the book you are looking at still has other connections. But he didn't explain the bitcoin process completely in just one book because the author's habit is usually to make readers come back to wait for the release of the next book and this is just my assumption. But if he says out of thin air that bitcoin has irreversibly regressed or collapsed in 2021, then I conclude he's not one of the authors worthy of being a favorite.
Why do I say that because he is too lazy to look for references regarding sources regarding Bitcoin's journey from when it was created to the process of its journey in the market until now. We know the four-year cycle in bitcoin and but to say that crypto in general has experienced a collapse is also wrong because the industry is basically growing.
In my opinion, the writer was just trying to write a book and didn't study the process properly from the beginning until they wrote the book and the writer missed a lot so that when he wrote the book it was based on what he knew and was not correct with exact certainty.
What you say is very correct, the author's lack of references means they write based on what they see and don't look for various references that make their writing appropriate to what is happening and I really believe in the four year cycle in Bitcoin and we can see in these few months the price of Bitcoin has experienced good improvement.