Comment by hombre_fatal

Then how does Siri deliver on that philosophy? The UX of Siri is that it probably won't understand your request but it might, and only through trial and error do you realize the specific commands it might know. And even then, your queries can fail for unknown reasons.

So I don't think this a likely explanation. Maybe they just wanted to have an in-house solution but realized they have no chance at delivering that value on their own. But it can't be about UX predictability because Siri has none unless you're setting a timer.