That is because there were a large number of accounts created at launch just to give MW3 a low score as soon as people could submit them.
I don't actually care
why people rate the game down or whether it perfectly matches up with "average mainstream opinion" or any other vague, non-existent abstraction of that sort -- it obviously doesn't, much like Metascore itself isn't an accurate reflection of the true critical quality of a title from an objective standpoint.
What's interesting about this metric is rather as a sniff-test for claims of fanbase unhappiness. In normal situations, games actually get almost exactly the same rating from fans as critics (look at all the games like Uncharted 2 or Mass Effect 2 that demonstrate close alignment between critics and fans.) When a game is sitting 20% lower with fans than critics, it speaks to some real, meaningful dissatisfactions amongst a portion of the fanbase (as happened with, say, GTA4.) When a game is looking at a 90+ Metascore and a 30-ish fan score, it means that fans (people who care enough to
buy the game) are also unhappy enough to spend time hunting down websites to trash the game on just out of a lack of any better way to express their displeasure.
So yes, I'm sure that the "real" "average" "rating" of the "mainstream" "audience" for MW3 wouldn't be exactly equivalent to 3.2, but it points to the level of irritation and dissatisfaction that dedicated fans are experiencing with the franchise at this point (and which, therefore, is probably starting to trickle out to more casual players.)
