sales performance is not a judge of game quality, it is a judge of a role being properly filled. There are plenty of things that people buy that aren't what they could be.
The problem with each of the games you mentioned is that they lacked what they could have been. There will be games in the future that do them one better because now people know that the market is there.
Wii fit sales do not make it good, having a cheap, fun way to exercise is what makes the sales. That doesn't mean that Wii fit is the best game it could possibly be, and that is what you don't understand about metacritic. It isn't about the "hardcore" demographic, it is about the game.
Look at spiderman 3, one of the biggest selling movies of all time, along with the new 3 star wars movies. Your logic would say that these are good movies, and film critics, those hardcore elitists, know nothing about what is popular.
