Tech accessories that don't play nicely with established human rules of etiquette have a much harder time being accepted, that's my theory. There's a long established history of reading or writing in public, and smartphones play nicely with all the etiquette that governs these activities in public.

Watches have etiquette too, primarily, it is seen as rude to check your while interacting with other people. So basically an apple watch is a device that you can't use in most of the situations where it would prove useful.

At the end of the day, where tech accessories are concerned, human social interactions are evolving much more slowly than the technology itself, and designers don't seem to really take this into account. Bluetooth headsets and Google Glass are two more great examples of what seems to be a failure to account for social rules and norms when they were designed.

I think the Watch is failing because it's not seen as essential, but more of a luxury toy. Putting aside the usefulness of it, and innovation, the phone has become so ingrained in the human psyche as the replacement to the watch that the bar to overcome is a bit high.