Easier sell than a relatively useless mobile-first HMD with so many tradeoffs between power, computing, and form factor it's not even funny. Much easier sell to wear glasses at a desk than a bulky headset into the world. With a tethered solution, power and computing does not have to be strapped to your head, mostly just optics.
Companies are so busy trying to turn AR into the next smartphone that they forget the display came first.