This review is obviously high effort. What's the incentive here? Is this what the community regularly does in Goodreads? Or are you somehow affiliated with the author and treat this as a favour?
High effort reviews are common on Goodreads, why? Because it's a community about passionate readers and probably those who write the very detailed reviews have enjoyed reading some other reviews and want to contribute back to the community. I think it's the same reason as people contributes to wikipedia: for the sake of sharing knowledge
It is an odd question on the internet where people regularly and normally put a lot of effort into reviews, blog posts, discussion forums comments and so on.
That coupled with question about affiliation probably makes people interpret is as not questions out of curiosity, but rather as sleazy way to introduce doubt on the author motivation.