Until now hardware has been too expensive and therefore relatively inaccessible. For example, Apple created a whole new software market (for apps) by making the iPhone hardware accessible. Once Google Glass gathers enough competition (in other words knockoffs) and prices come way down, as well as some kind of standards emerge (think Android OS), then we should be able to see some serious uptake and more traction for augmented reality.
See also my answer to:
· What types of applications would you like to see for the Google AR Glasses?