I don't think it's necessary to resort to evolutionary-biology explanations for that.
When I use voice to set my alarm, it's usually because my phone isn't in my hand. Maybe it's across the room from me. And speaking to it is more efficient than walking over to it, picking it up, and navigating to the alarm-setting UI. A voice command is a more streamlined UI for that specific task than a GUI is.
I don't think that example says much about chatbots, really, because the value is mostly the hands-free aspect, not the speak-it-in-English aspect.