I think that it's because people who just played a game and thought it was "just ok" won't feel the need to voice any opinion about it, leaving us with only good or bad opinions holders.

I mean, i kinda liked some games, like idk... Tomb Raider i guess? I don't know what i could say about it, t'was ok.

It doesn't sound as appealing as me saying GTA V single player was severely disappointing considering the massive steps made by other games of the same franchise.

Or that Metal Gear Solid V was one of the best games i played in the year it was released.