Then again, it seems not a lot of people are using the rating system to much extent anyway.
This.
Of course it is a bit of a feedback loop. There are people not using it because the reviews are not public. So why bother writing one.
To clarify: on Itch a rating is a review without text. A review is a rating with text. (At least that is how I understood it. They are used interchangeably often.)
Anyone wanting to see an overview can do so on the global feed.
https://itch.io/feed?filter=ratings
And, well, a short skimming on that says:
no 2 star, no 3 star 80% 5 star 10% 1 star 10% 4 star. And maybe 5% have text.
If no one uses 2 or 3 and rarely 4 star, they could just as well switch to positive and negative like Steam did. I see merit in this. It is not "perfect", but it has about the same information value as a 5 star rating system.
Maybe jam ratings are a bit more nuanced since the games therein do compete with each other and you have something to compare the games to.