And like many ratings sites BGG ends up weighted to novelty. Is this really the best movie / novel / video game / comic book / burger ? No, probably not, but it's the popular new one right now among people who watched a lot of movies, read a lot of novels, played a lot of video games, read a lot of comic books or ate a lot of burgers as appropriate.

Unlike built-in ratings (e.g. Uber, eBay) these ratings do at least provide some value at the low end. There are a fair few games on BGG with 5.0 or lower ratings and you probably just don't want those games, sight unseen.