Similarly for Kindle Unlimited despite the fact that Amazon clearly has the technology to address Markov Chain generated fakes, plagiarism and upvoting and review cabals, Amazon either chooses not to invest or not to invest enough to prevent all of that bad behavior.

IMHO investing 1/2 of 1% of the KU pool is enough to fund human review via their Mechanical Turk program. It wouldn't be perfect but it would eliminate most of the fraud.