The leading issue is this: people are morons. I mean, real stone-cold idiots.
Reviewers are paid because they can express their opinion well in a written form, not because they have a divine mandate to reinforce the popular opinion.
Moreover, review scores are stupid. A 7 in one publication is not the same as a 7 in another, and for fuck's sake don't start making conversion charts and begin trying to explain how a 3/5 is really only a 6/10 and blah blah blah. Publications define what those numbers mean within the context of their own reviewers - which people always ignore anyway - and even then you're dealing with different people within a publication.
And just to reinforce it: reviews are opinions. That's it. Objectivity only factors in to the extent of someone not taking a bribe to give a good score, or not being friends with someone who's worked on the game. The rest is just what people think, and no publication mandates stuff like, "a game must get a minimum of Score X if it has only 3 bugs". If someone hates The Last of Us then they're well within their rights to give it a fucking zero. This is not a difficult concept, this is what you learn when you're 6 and it becomes apparent that not everyone thinks the same way as you do.
Of course, all of this would be solved if reviewers simply gave a sentence-long, spoiler-free summary of their thoughts on any given game at the end of their review instead of using numbers, but then that'd be way too easy.