I've come to the (sad) conclusion that review systems are inaccurate, even when well intended. There was likely a moment during their existence where they were accurate. I would guesstimate this moment is generally before it gained momentum. E.g. early days of IMDB, early days of Amazon, and early days of tbat German law mentioned earlier (I don't know the name).
Since Metacritic is an aggregation of paid and amateur reviewers alike, it might very well be more accurate.
I really think GoodReads is the exception to this though. When I look through other people’s ratings I frequently see them using the full spectrum.
Furthermore, it’s very common for written reviews to say that a book really deserves some fractional number of stars, but Goodreads forced them to round.
Of course, the average ratings suck anyway...
This is particularly pronounced whenever there are any consequences attached to the ratings. If you give anything but 5 to your Uber driver, you're risking them losing their job. If you give anything but 5 on an e-commerce platform, the seller may lose a lot of money. 5 being the "neutral" score became normalized.