It isn't. The Apple Watch is a miniature computer on your wrist where the watch application is just one app among many. . . just as the iPhone is a complete miniature computer that also happens to make phone calls.
A true wrist watch merely tells various forms of time, including those that show phases of the moon, have a day and date feature, or help you calculate speed as a function of time over a measured distance.
That's the standard line when someone compares it to a conventional watch.
Now, someone questions why it doesn't have features normally found on other mobile computing devices, it's suddenly not fair that they aren't asking the same questions about conventional watches.