Same on IMDB, and even Rotten Tomatoes. There's a lot of money in movies. But books?
Online reviews don't have enough control over their reviewers and so it only takes a small number of unethical people to cause a big problem.
Books were $28,100,000,000 last year in the United States alone.
Audiobooks: $1,800,000,000
e-Books: $191,000,000
https://www.statista.com/topics/1177/book-market/#topicOverv...
Generally less money, yes. But not all motives are financial. And there are loads of conflict, drama, and emotions in many parts of the writing world.
I wish there was a modern equivalent.
... But when you're an incumbent that's likely to be around for at least a quarter of a decade with a sizeable monopoly, later really is better than never.