I used to think that too, but sometimes it’s more convenient to just glance at your wrist, rather than stop what you’re doing to dig out your phone, and press a button.
So I dug a couple of old Seikos out of a drawer and had the batteries replaced. Wearing one right now.
According to reports, ios 8 has code for environmental sensor (temp, barometric [alt, depth], humidity), a watch would be a good place for them.
If you have been retired long enough all you need is the sun, as a bonus, on cloudy days you get to sleep longer.