Back when the Wii was released, Red Steel sold so well because one of the first genres people thought could benefit from the Wiimote was First Person Shooters primarily because of the IR-pointing ... Since then few games/series in the genre have been handled in a way to actually attract customers.
Now, in relation to Call of Duty's performance ... One thing people have to remember is that the number of people who search for reviews on the internet prior to buying a game is actually very small. The most important factors that lead to people buying a game are prior experience with the series, word of mouth and marketing. Call of Duty 3 wasn't a particularly good game and when you factor in those that bought it new (or used), rented it, borrowed it from a friend, or stole it there are Millions of people out there who (potentially) have a lot of bad experiences with Call of Duty games on the Wii ... when you also add that the best game in the series (Call of Duty 4) didn't even get a third rate port to the Wii, and the marketing for the Wii version made it look like a light gun game, Activision has really screwed up with the Wii version which has probably cost them tens of millions of dollars.