Happened to me when I saw a book on the US site, I wasn’t able to see all reviews, but there was a button to sort-of “apply” to get approved for seeing all of them.
It took five days, then I got this email.
Interestingly, they’re not doing this on the European site, you can still see all reviews there.
I’d bet this is a move to prevent their reviews from being used to train competing AI systems.
Write product reviews using Amazon reviews, stuff with affiliate link, profit
Cognitive dark foresty
Or possibly if a product gets a lot of reviews in a short time, to prevent review bombing