Because I wear a nice watch already. It only tells the time, but it's also jewelry. A lot of us still want a mechanical watch on our wrists.
So where does that leave us if we also want what the Apple Watch offers, but aren't willing to displace our nice analog timepieces?
Sure, I could make an Apple PocketWatch (and it's tempting, since iPhone is now available only in "big" or "huge") but one of the most interesting things is the sensors on your skin and vibration as notification.
Maybe you could wear it on your ankle like a convict under house arrest?