> I'd like to know how it's possible for third-party sites such as https://www.fakespot.com to more effectively identify fake Amazon reviews while Amazon (with presumably better data) fails so miserably.

Maybe they can't? Fakespot authoritatively scores reviews but is there evidence that they are accurate? Anecdotally, there are many claims that the results aren't perfect, such as poor scores on a product where the seller knows there are no fake reviews. As a buyer the results on similar, shortlisted, products often seem a bit random compared to my judgement from reading the reviews carefully. Also, without knowing what reviews are identified and removed by amazon themselves we don't have much to compare it to.