I think you can explain much of the lack of lower scores by the fact that the games that would get lower scores are also likely to be ignored by just about any established reviewer.

There are thousands of games released every year that a site like IGN will never review. Would you find it valuable for IGN to scour Steam or the Switch eShop for terrible games just to use more of the score scale?

You may notice that this parallels the american school grading system to a T. Most major gaming review sites and such are done by americans that spent anywhere between 4-10+ years with that being the what grading/reviewing/scoring was done in almost every interaction they ever had past childhood, there's no wonder it's the standard here even if it's changed the scoring paradigm.

Find an independent critic you respect and listen to the tenor of why they say a game is good. Or ignore critics and develop your own taste and sense of which studios, directors, artists, composers, or otherwise will compel you to buy a game.

i use word of mouth mostly but its not that all critics are bad, just what seems like most, but if you find that you consistently align with a critics opinion I'd trust them