I suppose it's a space consideration, possibly - and maybe the sheer amount of energy required may be a lot more than a mere watch needs.
I only really wear a watch on the ferry these days, so that I have the time when the phone is off (to stop it hunting for a connection endlessly).
I like the idea of the kinetic watch, but wonder how long it would run, if I didn't wear it much.
There was a solar-powered, radio controlled watch that took my fancy. Always right, and it would stay going when you weren't wearing it.
I do have a mechanical watch with an alarm, which is handy.
The top winder charges and controls the alarm, the bottom does the watch, as normal. The alarm is set at around twenty to six here.