The numbers just don't say that much, users or critics. Hell, all amazon reviews are at least four stars.
I have the same problem on Yelp. I've had 1 star meals in 3 star restaurants and 3 star meals in places that get 5 stars "for their decor." When I'm hungry, the decor could be on fire for all I care.
People just like different aspects of games. FattiesGW didn't enjoy the demo and that should stand on its own as an argument. I know demos aren't perfect, but even the highest rated games aren't for everyone, and mid and low rated games have their appeal and their audience.
I'm sure if GTA5 had gotten 7s and 6s it still would've sold out, just like Call of Duty Ghosts has. I doubt any review could have stopped me from buying A Link Between Worlds and my rating for that is off the charts.
PSN: moothemagiccow (duh)