“explain why there are not only so few games prior to Kinect”
Because it’s a useless feature no one uses? Madden did it with a headset and dropped it the following year. Binary Domain used it. Some PS2 games used it. This is not some hugely special thing. Kinect isn’t doing anything special with voice.
“there aren’t any games that have had voice recognition added as an update after release for anything other than Kinect?”
See above. Microsoft goes to Studio A, and says, “Hey, we really need some Kinect features to advertise.” Studio A realizes motion controls would bork their game, so they come up with, “Voice controls!”
The NES had voice control via Konami’s headset. No one uses it because it never works well, and it’s easier to map those functions to the d-pad, not because of any technical hurdle.