tl;dr They're not personal assistants.
Siri, Google Assistant, Cortana, Alexa, etc.. The generic term is "personal assistants," but that's just a metaphor, like "virtual reality". In my opinion, a personal assistant, human or otherwise, must be able to do hear and form a respone to the following in a reasonable amount of time:
- "Where did I save that podcast I started listening to yesterday?"
- "Who was I going to call?"
- "Call them and ask for a refund."
- "Send Chris this photo via Hangouts."
- "Turn on my desktop and send me the Excel version of this Google Sheet that I'd saved on it."