Because if you read the reviews and played the game, you then realize it.
Also because I'm sure no one got the time to sit and play 60 hrs of a jRPG nowdays. So if you're not an honest writer, like Edge's reviewers are, you're gonna screw for sure. And they did screw big this time, alot of them. For the sake of clicks or of their ego. Luckily a great part of players, that have more time with them and are for the most more honest people (for obvious reasons), are widely liking LR:FFXIII. It's a typical game downvoted by "critics" (lol) and appreciated by the community. I anticipated this in the past: it's like NiER and Demon Souls, nothing less, nothing more.
The community in question may disagree with that statement (unless you are willing to go as far as dismissing the opinion of NeoGAF members who do not share your view on the subject).
Also, a big script doesn't necessarily mean a good plot. There is no correlation here.