The voice assistants are too basic. As folks have said before, nobody trusts Alexa to place orders. But if Alexa was as competent as an intelligent & capable human secretary, you would never interact with Amazon.com again.
Would you not, though? Don't the large majority of people, and dare I say probably literally everyone who buys something off Amazon first check the actual listing before buying anything?
I wouldn't trust any kind of AI bot regardless of intelligence or usefulness to buy toilet paper blindly, yet alone something like a hard drive or whatever.