I think it complements your phone. So it is more convenient to glance at your wrist than rooting around in your pocket and getting your phone out, something some people find quite rude.

If the trends reversed and they shrunk phones (like they did in the 90s) and put a strap on them, then they could easily replace the watch. But then battery life would be abysmal.

You can quickly see notifications. I also cannot see myself using Maps or looking at photos on the tiny screen. I would pull out my phone to do that, which i would have to wear with me anyway.

Not for you and me, I guess, but most women have a large, crowded bag instead of pockets. Which also explains how anyone could ever carry a Note around.