That might make sense for electronics and other items, though even here sellers have found ways to get around it by offering to reimburse their shills who bought the product just for a 5-star shill review.
However, Amazon's introduction of the Verified Purchase tag on reviews and recent changes that make non-VP reviews difficult to view, has had a deleterious effect on reviews for books, films and music. There were a lot of great well-written and insightful reviews written by people who got the media in question from the library (or a filesharing community). For books and films, that reviewing culture lives on at Goodreads and IMDB, but both are now owned by Amazon and who knows how long those reviews might last. There is however no analogue for reviews of music (Allmusic has strict character count limits and few ever go there, Discogs reviews seem mainly meant for vinyl enthusiasts).
Yes, in retrospect it was silly for fans of music, books and films to create a rather non-commercial community of enthusiasts on the basis of a site whose sole aim is to make lots of money, but I still regret what has been lost.