I'm not entirely convinced Apple even wants it to succeed. It's a stepping stone to augmented reality and a true 'forget you are wearing it' type of glasses product that can just naturally complement your surroundings.
I don't think anyone truely thinks people are going to all go to work, strap on a headset and be disconnected from their surroundings all day, that's never going to be a thing. Popping on a pair of glasses however is a much more approachable and user friendy experience, we're just not there yet.
There have been smart glasses made by Snapchat and Facebook, those didn't take off either.
Glasses are not visually subtle in the way smartwatches and phones are. It's one thing for everybody to be carrying the same iPhone, but people won't wear identical one-design-fits-all glasses when out and about.
For glasses, people will care more about how it looks than what it does. The fashion barrier is something that designers have not put enough thought into and unsurprisingly, they haven't taken off.
I don't think anyone truely thinks people are going to all go to work, strap on a headset and be disconnected from their surroundings all day, that's never going to be a thing. Popping on a pair of glasses however is a much more approachable and user friendy experience, we're just not there yet.