I think it has more to do with the fact that we have the attention span of gnats.
I think that the vast majority would rather have a pretty game that you don't have to think too much about to beat. For most people it's a fast paced world and the image of a pretty game with pretty simple game play and a pretty simple plot is appealing to the masses who simply don't want to invest a massive amount of time in a video game.
I watch my nephew play his games and it's pretty evident. He'll play Metroid Prime as long as it's "running, jumping, hitting switches," but throw a boss at him and if he can't figure it out he just stops playing. He has a pretty good selection of games, but hasn't beaten a single one. When he invites friends over, it's the same thing. If it can't be beaten in an hour or two then it's not worth the time.
There are a select few of us, who relish the thought of spending days playing the same video game. We like the tough boss battles that make you think, we like the long intricate plots and we despise the "switch puzzles." I like to play Halo on the hardest level. Most times I get my ass handed to me, but I always come back.
We live in a "blip" world. For video game companies to compete for that sainted demographic, they have to put out sub-standard stuff. It's what keeps the kids happy.