No-one is mentioning the form-factor.
Its truly awful for a computing display device more complicated than telling the time.
Ok, you might get the fitness/heart rate gang, maybe the stock tickers too, but its mostly good for output only, and even then, a hi-res display just sucks a lot of power that simply isn't plentiful enough.
A classic analogue watch with perhaps a bit of bluetooth alarm-ery built in could work. A wrist-sized computing device is going to be (to put it kindly) ahead of its time.