To be fair, there is a story mode in the DS Taiko games. I mean, they are basically play a song, fight the boss or whatever, do this do that, but I guess you can call it a narrative.
Hence: "to a lesser extent". Hell, DDR has a story mode in some of the console versions.
And as to why a game with Miku's mere presense that also has her name sharing a title has me turned off of it; it's because it's a very weird fucking thing.
The idea of a vocaloid, a character that exists in the world without narrative or characterization and is only given context by it's fandom is difficult to process. Putting my opinions on it off to the side, it's pretty easy to see why most people wouldn't "get it". Even with stuff like Black Rock Shooter, which is a bizzare concept in itself, Miku, as an actress or as the lead in that movie, has some sort of characterization, something for people to connect with other than her character design.
So then you have this game, which seems to basically ask the audience to connect with Miku and the other vocaliods, solely for their artstyle, and that's a very strange thing to ask in a video game. And the gameplay element of the game aren't so dominating that the game allows Miku to drop into the background. Even while playing and reserving your attention for concentation, the game demands that you give Miku your full attention through the reasons I've already stated.
It's a very weird fuckin' thing. I'm not even saying that it's necessarily bad. But I am saying that it's a difficult thing for people who aren't fully indoctrinated into what Miku..."is" to get into this game. And for me personally, the focus on Miku over gameplay is a turn off.
It's such a strange thing. Interestingly enough, something like Space Channel 5 would probably get me into her more readily. But this game seems like you're jumping into the deep end of the vocaloid fan machine and...that's not something I'm ready to do, nor do I think most others are.
I guess, If I had to some up why this game puts me off, it is it's glaring lack of an answer to the question, "why?".
Perhaps that's the better course of action right now.
Sell me on this game. Why should I care about this besides the fact that it seems like a competent rhythm game on a handheld console that respects my time?