Why no more iPod music games?

I was thinking about Phase, the iPod game, and wondering why there aren't more music related games for the iPod platform? The interface is simple and easy and there are lots of possibilities. Why not a kind of electroplankton for the iPod where you can adapt to interact with the music on your iPod using an interface like that of electroplankton?

Or for that matter something like Jam Sessions? Play along to your fav tracks?

Perhaps we'll see more thing like this once the iPhone /iPod Touch SDK is released into the wild and more developers can start to make interesting things for that platform. I do hope so.