I don't like it either but I understanding it.
For the average consumer those are names they know and they like to play, even if the changes are small each year the story its different and that's what their friends are playing online so its a win-win situation for them. The game themselves may not be great every year but are never bad. Also they brag about being hardcore for buying every game in X franchise and playing it a lot.
From the point of view of the companies they want their games to sell a lot, and they know they can get away with it for some time because of the reasons above.
Now there its a crowd that may not seem as much but are actually really smart when it comes to buying yearly edition games, the casual wii crowd, they will not buy the same game every year, they have a gaming need (be it a FPS, a RPG, a Guitar hero game, a racing games, etc) so they buy that game and stick to it and rarelly buy the next game in the franchise, it has happenend before and will happen again (with Just Dance for example, the next game may not be a huge seller as Ubisoft its burning the franchise to the ashes) that's the reason Nintendo doesn't release more than 1 Super Smash or Mario Kart per generation, never discount the games and creates new advertisement every year for the same old games.
