Do you live alone? If anyone else lives with you, how do they have this kind of experience when your iPhone is out of the house with you? What do they do when you are away for a week or two for vacation/travel?
It's the same argument made against, "why can't our iPhones be the

TV remote?" It can. But again, that's great for singles living alone... but as soon as the "remote" leaves the home, how do the rest back at home control the

TV?
This- like

TV- is primarily meant to be a
stationary (at home) device... not a mobile device that may or may not be at home at any given time.
Note: I've been fairly skeptical about the merits of one of these myself... until I'm at friends homes with one of the competitor's versions. They use them a lot and competitor devices seem almost Star-Trekkian "computer..." useful and very simple to use. Several of these friends have iPhones but still favor Echo vs. "Hey Siri...". Siri will have to make some big strides to seem as good IMO.