Personally I think it was the camera that killed it. That, and the fact that google put out an unfinished product without providing plethora of resources and apps for it, to get people excited, hoping the community would finish it for them... That, and the fact that people started calling Google Glass users "glassholes".
That was one weird thing I did not expect to happen after the release, but I can't stop thinking that a people calling Glass wearers "glassholes" are themselves actual assholes.